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---
layout: "docs"
page_title: "Configuration"
sidebar_current: "docs-agent-config"
description: |-
The agent has various configuration options that can be specified via the command-line or via configuration files. All of the configuration options are completely optional. Defaults are specified with their descriptions.
---
# Configuration
The agent has various configuration options that can be specified via
the command-line or via configuration files. All of the configuration
options are completely optional. Defaults are specified with their
descriptions.
When loading configuration, Consul loads the configuration from files
and directories in lexical order. For example, configuration file `basic_config.json`
will be processed before `extra_config.json`. Configuration specified later
will be merged into configuration specified earlier. In most cases,
"merge" means that the later version will override the earlier. In
some cases, such as event handlers, merging appends the handlers to the
existing configuration. The exact merging behavior is specified for each
option below.
Consul also supports reloading configuration when it receives the
SIGHUP signal. Not all changes are respected, but those that are
are documented below in the
[Reloadable Configuration](#reloadable-configuration) section. The
[reload command](/docs/commands/reload.html) can also be used to trigger a
configuration reload.
## Command-line Options
The options below are all specified on the command-line.
* <a name="_advertise"></a><a href="#_advertise">`-advertise`</a> - The advertise
address is used to change the address that we
advertise to other nodes in the cluster. By default, the [`-bind`](#_bind) address is
advertised. However, in some cases, there may be a routable address that cannot
be bound. This flag enables gossiping a different address to support this.
If this address is not routable, the node will be in a constant flapping state
as other nodes will treat the non-routability as a failure.
* <a name="_advertise-wan"></a><a href="#_advertise-wan">`-advertise-wan`</a> - The
advertise WAN address is used to change the address that we advertise to server nodes
joining through the WAN. This can also be set on client agents when used in combination
with the <a href="#translate_wan_addrs">`translate_wan_addrs`</a> configuration
option. By default, the [`-advertise`](#_advertise) address is advertised. However, in some
cases all members of all datacenters cannot be on the same physical or virtual network,
especially on hybrid setups mixing cloud and private datacenters. This flag enables server
nodes gossiping through the public network for the WAN while using private VLANs for gossiping
to each other and their client agents, and it allows client agents to be reached at this
address when being accessed from a remote datacenter if the remote datacenter is configured
with <a href="#translate_wan_addrs">`translate_wan_addrs`</a>.
* <a name="_atlas"></a><a href="#_atlas">`-atlas`</a> - This flag
enables [Atlas](https://atlas.hashicorp.com) integration.
It is used to provide the Atlas infrastructure name and the SCADA connection. The format of
this is `username/environment`. This enables Atlas features such as the Monitoring UI
and node auto joining.
* <a name="_atlas_join"></a><a href="#_atlas_join">`-atlas-join`</a> - When set, enables auto-join
via Atlas. Atlas will track the most
recent members to join the infrastructure named by [`-atlas`](#_atlas) and automatically
join them on start. For servers, the LAN and WAN pool are both joined.
* <a name="_atlas_token"></a><a href="#_atlas_token">`-atlas-token`</a> - Provides the Atlas
API authentication token. This can also be provided
using the `ATLAS_TOKEN` environment variable. Required for use with Atlas.
* <a name="_atlas_endpoint"></a><a href="#_atlas_endpoint">`-atlas-endpoint`</a> - The endpoint
address used for Atlas integration. Used only if the `-atlas` and
`-atlas-token` options are specified. This is optional, and defaults to the
public Atlas endpoints. This can also be specified using the `SCADA_ENDPOINT`
environment variable. The CLI option takes precedence, followed by the
configuration file directive, and lastly, the environment variable.
* <a name="_bootstrap"></a><a href="#_bootstrap">`-bootstrap`</a> - This flag is used to control if a
server is in "bootstrap" mode. It is important that
no more than one server *per* datacenter be running in this mode. Technically, a server in bootstrap mode
is allowed to self-elect as the Raft leader. It is important that only a single node is in this mode;
otherwise, consistency cannot be guaranteed as multiple nodes are able to self-elect.
It is not recommended to use this flag after a cluster has been bootstrapped.
* <a name="_bootstrap_expect"></a><a href="#_bootstrap_expect">`-bootstrap-expect`</a> - This flag
provides the number of expected servers in the datacenter.
Either this value should not be provided or the value must agree with other servers in
the cluster. When provided, Consul waits until the specified number of servers are
available and then bootstraps the cluster. This allows an initial leader to be elected
automatically. This cannot be used in conjunction with the legacy [`-bootstrap`](#_bootstrap) flag.
* <a name="_bind"></a><a href="#_bind">`-bind`</a> - The address that should be bound to
for internal cluster communications.
This is an IP address that should be reachable by all other nodes in the cluster.
By default, this is "0.0.0.0", meaning Consul will use the first available private
IPv4 address. If you specify "[::]", Consul will use the first available public IPv6 address.
Consul uses both TCP and UDP and the same port for both. If you
have any firewalls, be sure to allow both protocols.
* <a name="_client"></a><a href="#_client">`-client`</a> - The address to which
Consul will bind client interfaces,
including the HTTP, DNS, and RPC servers. By default, this is "127.0.0.1",
allowing only loopback connections. The RPC address is used by other Consul
commands, such as `consul members`, in order to query a running Consul agent.
* <a name="_config_file"></a><a href="#_config_file">`-config-file`</a> - A configuration file
to load. For more information on
the format of this file, read the [Configuration Files](#configuration_files) section.
This option can be specified multiple times to load multiple configuration
files. If it is specified multiple times, configuration files loaded later
will merge with configuration files loaded earlier. During a config merge,
single-value keys (string, int, bool) will simply have their values replaced
while list types will be appended together.
* <a name="_config_dir"></a><a href="#_config_dir">`-config-dir`</a> - A directory of
configuration files to load. Consul will
load all files in this directory with the suffix ".json". The load order
is alphabetical, and the the same merge routine is used as with the
[`config-file`](#_config_file) option above. This option can be specified multiple times
to load multiple directories. Sub-directories of the config directory are not loaded.
For more information on the format of the configuration files, see the
[Configuration Files](#configuration_files) section.
* <a name="_data_dir"></a><a href="#_data_dir">`-data-dir`</a> - This flag provides
a data directory for the agent to store state.
This is required for all agents. The directory should be durable across reboots.
This is especially critical for agents that are running in server mode as they
must be able to persist cluster state. Additionally, the directory must support
the use of filesystem locking, meaning some types of mounted folders (e.g. VirtualBox
shared folders) may not be suitable.
* <a name="_dev"></a><a href="#_dev">`-dev`</a> - Enable development server
mode. This is useful for quickly starting a Consul agent with all persistence
options turned off, enabling an in-memory server which can be used for rapid
prototyping or developing against the API. This mode is **not** intended for
production use as it does not write any data to disk.
* <a name="_datacenter"></a><a href="#_datacenter">`-datacenter`</a> - This flag controls the datacenter in
which the agent is running. If not provided,
it defaults to "dc1". Consul has first-class support for multiple datacenters, but
it relies on proper configuration. Nodes in the same datacenter should be on a single
LAN.
* <a name="_domain"></a><a href="#_domain">`-domain`</a> - By default, Consul responds to DNS queries
in the "consul." domain. This flag can be used to change that domain. All queries in this domain
are assumed to be handled by Consul and will not be recursively resolved.
* <a name="_encrypt"></a><a href="#_encrypt">`-encrypt`</a> - Specifies the secret key to
use for encryption of Consul
network traffic. This key must be 16-bytes that are Base64-encoded. The
easiest way to create an encryption key is to use
[`consul keygen`](/docs/commands/keygen.html). All
nodes within a cluster must share the same encryption key to communicate.
The provided key is automatically persisted to the data directory and loaded
automatically whenever the agent is restarted. This means that to encrypt
Consul's gossip protocol, this option only needs to be provided once on each
agent's initial startup sequence. If it is provided after Consul has been
initialized with an encryption key, then the provided key is ignored and
a warning will be displayed.
* <a name="_http_port"></a><a href="#_http_port">`-http-port`</a> - the HTTP API port to listen on.
This overrides the default port 8500. This option is very useful when deploying Consul
to an environment which communicates the HTTP port through the environment e.g. PaaS like CloudFoundry, allowing
you to set the port directly via a Procfile.
* <a name="_join"></a><a href="#_join">`-join`</a> - Address of another agent
to join upon starting up. This can be
specified multiple times to specify multiple agents to join. If Consul is
unable to join with any of the specified addresses, agent startup will
fail. By default, the agent won't join any nodes when it starts up.
* <a name="_retry_join"></a><a href="#_retry_join">`-retry-join`</a> - Similar
to [`-join`](#_join) but allows retrying a join if the first
attempt fails. This is useful for cases where we know the address will become
available eventually.
* <a name="_retry_interval"></a><a href="#_retry_interval">`-retry-interval`</a> - Time
to wait between join attempts. Defaults to 30s.
* <a name="_retry_max"></a><a href="#_retry_max">`-retry-max`</a> - The maximum number
of [`-join`](#_join) attempts to be made before exiting
with return code 1. By default, this is set to 0 which is interpreted as infinite
retries.
* <a name="_join_wan"></a><a href="#_join_wan">`-join-wan`</a> - Address of another
wan agent to join upon starting up. This can be
specified multiple times to specify multiple WAN agents to join. If Consul is
unable to join with any of the specified addresses, agent startup will
fail. By default, the agent won't [`-join-wan`](#_join_wan) any nodes when it starts up.
* <a name="_retry_join_wan"></a><a href="#_retry_join_wan">`-retry-join-wan`</a> - Similar
to [`retry-join`](#_retry_join) but allows retrying a wan join if the first attempt fails.
This is useful for cases where we know the address will become
available eventually.
* <a name="_retry_interval_wan"></a><a href="#_retry_interval_wan">`-retry-interval-wan`</a> - Time
to wait between [`-join-wan`](#_join_wan) attempts.
Defaults to 30s.
* <a name="_retry_max_wan"></a><a href="#_retry_max_wan">`-retry-max-wan`</a> - The maximum
number of [`-join-wan`](#_join_wan) attempts to be made before exiting with return code 1.
By default, this is set to 0 which is interpreted as infinite retries.
* <a name="_log_level"></a><a href="#_log_level">`-log-level`</a> - The level of logging to
show after the Consul agent has started. This defaults to "info". The available log levels are
"trace", "debug", "info", "warn", and "err". Note that you can always connect to an
agent via [`consul monitor`](/docs/commands/monitor.html) and use any log level. Also, the
log level can be changed during a config reload.
* <a name="_node"></a><a href="#_node">`-node`</a> - The name of this node in the cluster.
This must be unique within the cluster. By default this is the hostname of the machine.
* <a name="_pid_file"></a><a href="#_pid_file">`-pid-file`</a> - This flag provides the file
path for the agent to store its PID. This is useful for sending signals (for example, `SIGINT`
to close the agent or `SIGHUP` to update check definite
* <a name="_protocol"></a><a href="#_protocol">`-protocol`</a> - The Consul protocol version to
use. This defaults to the latest version. This should be set only when [upgrading](/docs/upgrading.html).
You can view the protocol versions supported by Consul by running `consul -v`.
* <a name="_recursor"></a><a href="#_recursor">`-recursor`</a> - Specifies the address of an upstream DNS
server. This option may be provided multiple times, and is functionally
equivalent to the [`recursors` configuration option](#recursors).
* <a name="_rejoin"></a><a href="#_rejoin">`-rejoin`</a> - When provided, Consul will ignore a
previous leave and attempt to rejoin the cluster when starting. By default, Consul treats leave
as a permanent intent and does not attempt to join the cluster again when starting. This flag
allows the previous state to be used to rejoin the cluster.
* <a name="_server"></a><a href="#_server">`-server`</a> - This flag is used to control if an
agent is in server or client mode. When provided,
an agent will act as a Consul server. Each Consul cluster must have at least one server and ideally
no more than 5 per datacenter. All servers participate in the Raft consensus algorithm to ensure that
transactions occur in a consistent, linearizable manner. Transactions modify cluster state, which
is maintained on all server nodes to ensure availability in the case of node failure. Server nodes also
participate in a WAN gossip pool with server nodes in other datacenters. Servers act as gateways
to other datacenters and forward traffic as appropriate.
* <a name="_syslog"></a><a href="#_syslog">`-syslog`</a> - This flag enables logging to syslog. This
is only supported on Linux and OSX. It will result in an error if provided on Windows.
* <a name="_ui"></a><a href="#_ui">`-ui`</a> - Enables the built-in web UI
server and the required HTTP routes. This eliminates the need to maintain the
Consul web UI files separately from the binary.
* <a name="_ui_dir"></a><a href="#_ui_dir">`-ui-dir`</a> - This flag provides the directory containing
the Web UI resources for Consul. This will automatically enable the Web UI. The directory must be
readable to the agent.
## <a name="configuration_files"></a>Configuration Files
In addition to the command-line options, configuration can be put into
files. This may be easier in certain situations, for example when Consul is
being configured using a configuration management system.
The configuration files are JSON formatted, making them easily readable
and editable by both humans and computers. The configuration is formatted
as a single JSON object with configuration within it.
Configuration files are used for more than just setting up the agent,
they are also used to provide check and service definitions. These are used
to announce the availability of system servers to the rest of the cluster.
They are documented separately under [check configuration](/docs/agent/checks.html) and
[service configuration](/docs/agent/services.html) respectively. The service and check
definitions support being updated during a reload.
#### Example Configuration File
```javascript
{
"datacenter": "east-aws",
"data_dir": "/opt/consul",
"log_level": "INFO",
"node_name": "foobar",
"server": true,
"watches": [
{
"type": "checks",
"handler": "/usr/bin/health-check-handler.sh"
}
],
"telemetry": {
"statsite_address": "127.0.0.1:2180"
}
}
```
#### Example Configuration File, with TLS
```javascript
{
"datacenter": "east-aws",
"data_dir": "/opt/consul",
"log_level": "INFO",
"node_name": "foobar",
"server": true,
"addresses": {
"https": "0.0.0.0"
},
"ports": {
"https": 8080
},
"key_file": "/etc/pki/tls/private/my.key",
"cert_file": "/etc/pki/tls/certs/my.crt",
"ca_file": "/etc/pki/tls/certs/ca-bundle.crt"
}
```
Note that the use of `port`:
```javascript
"ports": {
"https": 8080
}
```
Consul will not enable TLS for the HTTP API unless the `https` port has been assigned a port number `> 0`.
#### Configuration Key Reference
* <a name="acl_datacenter"></a><a href="#acl_datacenter">`acl_datacenter`</a> - Only
used by servers. This designates the datacenter which
is authoritative for ACL information. It must be provided to enable ACLs.
All servers and datacenters must agree on the ACL datacenter. Setting it on
the servers is all you need for enforcement, but for the APIs to forward properly
from the clients, it must be set on them too. Future changes may move
enforcement to the edges, so it's best to just set `acl_datacenter` on all nodes.
* <a name="acl_default_policy"></a><a href="#acl_default_policy">`acl_default_policy`</a> - Either
"allow" or "deny"; defaults to "allow". The default policy controls the behavior of a token when
there is no matching rule. In "allow" mode, ACLs are a blacklist: any operation not specifically
prohibited is allowed. In "deny" mode, ACLs are a whitelist: any operation not
specifically allowed is blocked.
* <a name="acl_down_policy"></a><a href="#acl_down_policy">`acl_down_policy`</a> - Either
"allow", "deny" or "extend-cache"; "extend-cache" is the default. In the case that the
policy for a token cannot be read from the [`acl_datacenter`](#acl_datacenter) or leader
node, the down policy is applied. In "allow" mode, all actions are permitted, "deny" restricts
all operations, and "extend-cache" allows any cached ACLs to be used, ignoring their TTL
values. If a non-cached ACL is used, "extend-cache" acts like "deny".
* <a name="acl_master_token"></a><a href="#acl_master_token">`acl_master_token`</a> - Only used
for servers in the [`acl_datacenter`](#acl_datacenter). This token will be created with management-level
permissions if it does not exist. It allows operators to bootstrap the ACL system
with a token ID that is well-known.
<br><br>
Note that the `acl_master_token` is only installed when a server acquires cluster leadership. If
you would like to install or change the `acl_master_token`, set the new value for `acl_master_token`
in the configuration for all servers. Once this is done, restart the current leader to force a
leader election. If the acl_master_token is not supplied, then the servers do not create a master
token. When you provide a value, it can be any string value. Using a UUID would ensure that it looks
the same as the other tokens, but isn't strictly necessary.
* <a name="acl_token"></a><a href="#acl_token">`acl_token`</a> - When provided, the agent will use this
token when making requests to the Consul servers. Clients can override this token on a per-request
basis by providing the "?token" query parameter. When not provided, the empty token, which maps to
the 'anonymous' ACL policy, is used.
* <a name="acl_ttl"></a><a href="#acl_ttl">`acl_ttl`</a> - Used to control Time-To-Live caching of ACLs.
By default, this is 30 seconds. This setting has a major performance impact: reducing it will cause
more frequent refreshes while increasing it reduces the number of caches. However, because the caches
are not actively invalidated, ACL policy may be stale up to the TTL value.
* <a name="addresses"></a><a href="#addresses">`addresses`</a> - This is a nested object that allows
setting bind addresses.
<br><br>
Both `rpc` and `http` support binding to Unix domain sockets. A socket can be
specified in the form `unix:///path/to/socket`. A new domain socket will be
created at the given path. If the specified file path already exists, Consul
will attempt to clear the file and create the domain socket in its place. The
permissions of the socket file are tunable via the [`unix_sockets` config construct](#unix_sockets).
<br><br>
When running Consul agent commands against Unix socket interfaces, use the
`-rpc-addr` or `-http-addr` arguments to specify the path to the socket. You
can also place the desired values in `CONSUL_RPC_ADDR` and `CONSUL_HTTP_ADDR`
environment variables.
<br><br>
For TCP addresses, these should simply be an IP address without the port. For
example: `10.0.0.1`, not `10.0.0.1:8500`. Ports are set separately in the
<a href="#ports">`ports`</a> structure.
<br><br>
The following keys are valid:
* `dns` - The DNS server. Defaults to `client_addr`
* `http` - The HTTP API. Defaults to `client_addr`
* `https` - The HTTPS API. Defaults to `client_addr`
* `rpc` - The CLI RPC endpoint. Defaults to `client_addr`
* <a name="advertise_addr"></a><a href="#advertise_addr">`advertise_addr`</a> Equivalent to
the [`-advertise` command-line flag](#_advertise).
* <a name="advertise_addrs"></a><a href="#advertise_addrs">`advertise_addrs`</a> Allows to set
the advertised addresses for SerfLan, SerfWan and RPC together with the port. This gives
you more control than <a href="#_advertise">`-advertise`</a> or <a href="#_advertise-wan">`-advertise-wan`</a>
while it serves the same purpose. These settings might override <a href="#_advertise">`-advertise`</a> or
<a href="#_advertise-wan">`-advertise-wan`</a>
<br><br>
This is a nested setting that allows the following keys:
* `serf_lan` - The SerfLan address. Accepts values in the form of "host:port" like "10.23.31.101:8301".
* `serf_wan` - The SerfWan address. Accepts values in the form of "host:port" like "10.23.31.101:8302".
* `rpc` - The server RPC address. Accepts values in the form of "host:port" like "10.23.31.101:8300".
* <a name="advertise_addr_wan"></a><a href="#advertise_addr_wan">`advertise_addr_wan`</a> Equivalent to
the [`-advertise-wan` command-line flag](#_advertise-wan).
* <a name="atlas_acl_token"></a><a href="#atlas_acl_token">`atlas_acl_token`</a> When provided,
any requests made by Atlas will use this ACL token unless explicitly overridden. When not provided
the [`acl_token`](#acl_token) is used. This can be set to 'anonymous' to reduce permission below
that of [`acl_token`](#acl_token).
* <a name="atlas_infrastructure"></a><a href="#atlas_infrastructure">`atlas_infrastructure`</a>
Equivalent to the [`-atlas` command-line flag](#_atlas).
* <a name="atlas_join"></a><a href="#atlas_join">`atlas_join`</a> Equivalent to the
[`-atlas-join` command-line flag](#_atlas_join).
* <a name="atlas_token"></a><a href="#atlas_token">`atlas_token`</a> Equivalent to the
[`-atlas-token` command-line flag](#_atlas_token).
* <a name="atlas_endpoint"></a><a href="#atlas_endpoint">`atlas_endpoint`</a> Equivalent to the
[`-atlas-endpoint` command-line flag](#_atlas_endpoint).
* <a name="bootstrap"></a><a href="#bootstrap">`bootstrap`</a> Equivalent to the
[`-bootstrap` command-line flag](#_bootstrap).
* <a name="bootstrap_expect"></a><a href="#bootstrap_expect">`bootstrap_expect`</a> Equivalent
to the [`-bootstrap-expect` command-line flag](#_bootstrap_expect).
* <a name="bind_addr"></a><a href="#bind_addr">`bind_addr`</a> Equivalent to the
[`-bind` command-line flag](#_bind).
* <a name="ca_file"></a><a href="#ca_file">`ca_file`</a> This provides a file path to a PEM-encoded
certificate authority. The certificate authority is used to check the authenticity of client and
server connections with the appropriate [`verify_incoming`](#verify_incoming) or
[`verify_outgoing`](#verify_outgoing) flags.
* <a name="cert_file"></a><a href="#cert_file">`cert_file`</a> This provides a file path to a
PEM-encoded certificate. The certificate is provided to clients or servers to verify the agent's
authenticity. It must be provided along with [`key_file`](#key_file).
* <a name="check_update_interval"></a><a href="#check_update_interval">`check_update_interval`</a>
This interval controls how often check output from
checks in a steady state is synchronized with the server. By default, this is
set to 5 minutes ("5m"). Many checks which are in a steady state produce
slightly different output per run (timestamps, etc) which cause constant writes.
This configuration allows deferring the sync of check output for a given interval to
reduce write pressure. If a check ever changes state, the new state and associated
output is synchronized immediately. To disable this behavior, set the value to "0s".
* <a name="client_addr"></a><a href="#client_addr">`client_addr`</a> Equivalent to the
[`-client` command-line flag](#_client).
* <a name="datacenter"></a><a href="#datacenter">`datacenter`</a> Equivalent to the
[`-datacenter` command-line flag](#_datacenter).
* <a name="data_dir"></a><a href="#data_dir">`data_dir`</a> Equivalent to the
[`-data-dir` command-line flag](#_data_dir).
* <a name="disable_anonymous_signature"></a><a href="#disable_anonymous_signature">
`disable_anonymous_signature`</a> Disables providing an anonymous signature for de-duplication
with the update check. See [`disable_update_check`](#disable_update_check).
* <a name="disable_remote_exec"></a><a href="#disable_remote_exec">`disable_remote_exec`</a>
Disables support for remote execution. When set to true, the agent will ignore any incoming
remote exec requests.
* <a name="disable_update_check"></a><a href="#disable_update_check">`disable_update_check`</a>
Disables automatic checking for security bulletins and new version releases.
* <a name="dns_config"></a><a href="#dns_config">`dns_config`</a> This object allows a number
of sub-keys to be set which can tune how DNS queries are serviced. See this guide on
[DNS caching](/docs/guides/dns-cache.html) for more detail.
<br><br>
The following sub-keys are available:
* <a name="allow_stale"></a><a href="#allow_stale">`allow_stale`</a> - Enables a stale query
for DNS information. This allows any Consul server, rather than only the leader, to service
the request. The advantage of this is you get linear read scalability with Consul servers.
By default, this is false, meaning all requests are serviced by the leader, providing stronger
consistency but less throughput and higher latency.
* <a name="max_stale"></a><a href="#max_stale">`max_stale`</a> When [`allow_stale`](#allow_stale)
is specified, this is used to limit how
stale results are allowed to be. By default, this is set to "5s":
if a Consul server is more than 5 seconds behind the leader, the query will be
re-evaluated on the leader to get more up-to-date results.
* <a name="node_ttl"></a><a href="#node_ttl">`node_ttl`</a> By default, this is "0s", so all
node lookups are served with a 0 TTL value. DNS caching for node lookups can be enabled by
setting this value. This should be specified with the "s" suffix for second or "m" for minute.
* <a name="service_ttl"></a><a href="#service_ttl">`service_ttl`</a> This is a sub-object
which allows for setting a TTL on service lookups with a per-service policy. The "*" wildcard
service can be used when there is no specific policy available for a service. By default, all
services are served with a 0 TTL value. DNS caching for service lookups can be enabled by
setting this value.
* <a name="enable_truncate"></a><a href="#enable_truncate">`enable_truncate`</a> If set to
true, a UDP DNS query that would return more than 3 records, or more than would fit into a valid
UDP response, will set the truncated flag, indicating to clients that they should re-query
using TCP to get the full set of records.
* <a name="only_passing"></a><a href="#only_passing">`only_passing`</a> If set to true, any
nodes whose health checks are warning or critical will be excluded from DNS results. If false,
the default, only nodes whose healthchecks are failing as critical will be excluded. For
service lookups, the health checks of the node itself, as well as the service-specific checks
are considered. For example, if a node has a health check that is critical then all services on
that node will be excluded because they are also considered critical.
* <a name="udp_answer_limit"></a><a
href="#udp_answer_limit">`udp_answer_limit`</a> - Limit the number of
resource records contained in the answer section of a UDP-based DNS
response. When answering a question, Consul will use the complete list of
matching hosts, shuffle the list randomly, and then limit the number of
answers to `udp_answer_limit` (default `3`). In environments where
[RFC 3484 Section 6](https://tools.ietf.org/html/rfc3484#section-6) Rule 9
is implemented and enforced (i.e. DNS answers are always sorted and
therefore never random), clients may need to set this value to `1` to
preserve the expected randomized distribution behavior (note:
[RFC 3484](https://tools.ietf.org/html/rfc3484) has been obsoleted by
[RFC 6724](https://tools.ietf.org/html/rfc6724) and as a result it should
be increasingly uncommon to need to change this value with modern
resolvers).
* <a name="domain"></a><a href="#domain">`domain`</a> Equivalent to the
[`-domain` command-line flag](#_domain).
* <a name="enable_debug"></a><a href="#enable_debug">`enable_debug`</a> When set, enables some
additional debugging features. Currently, this is only used to set the runtime profiling HTTP endpoints.
* <a name="enable_syslog"></a><a href="#enable_syslog">`enable_syslog`</a> Equivalent to
the [`-syslog` command-line flag](#_syslog).
* <a name="encrypt"></a><a href="#encrypt">`encrypt`</a> Equivalent to the
[`-encrypt` command-line flag](#_encrypt).
* <a name="key_file"></a><a href="#key_file">`key_file`</a> This provides a the file path to a
PEM-encoded private key. The key is used with the certificate to verify the agent's authenticity.
This must be provided along with [`cert_file`](#cert_file).
* <a name="http_api_response_headers"></a><a href="#http_api_response_headers">`http_api_response_headers`</a>
This object allows adding headers to the HTTP API
responses. For example, the following config can be used to enable
[CORS](https://en.wikipedia.org/wiki/Cross-origin_resource_sharing) on
the HTTP API endpoints:
```javascript
{
"http_api_response_headers": {
"Access-Control-Allow-Origin": "*"
}
}
```
* <a name="leave_on_terminate"></a><a href="#leave_on_terminate">`leave_on_terminate`</a> If
enabled, when the agent receives a TERM signal,
it will send a `Leave` message to the rest of the cluster and gracefully
leave. Defaults to false.
* <a name="log_level"></a><a href="#log_level">`log_level`</a> Equivalent to the
[`-log-level` command-line flag](#_log_level).
* <a name="node_name"></a><a href="#node_name">`node_name`</a> Equivalent to the
[`-node` command-line flag](#_node).
* <a name="ports"></a><a href="#ports">`ports`</a> This is a nested object that allows setting
the bind ports for the following keys:
* <a name="dns_port"></a><a href="#dns_port">`dns`</a> - The DNS server, -1 to disable. Default 8600.
* <a name="http_port"></a><a href="#http_port">`http`</a> - The HTTP API, -1 to disable. Default 8500.
* <a name="https_port"></a><a href="#https_port">`https`</a> - The HTTPS API, -1 to disable. Default -1 (disabled).
* <a name="rpc_port"></a><a href="#rpc_port">`rpc`</a> - The CLI RPC endpoint. Default 8400.
* <a name="serf_lan_port"></a><a href="#serf_lan_port">`serf_lan`</a> - The Serf LAN port. Default 8301.
* <a name="serf_wan_port"></a><a href="#serf_wan_port">`serf_wan`</a> - The Serf WAN port. Default 8302.
* <a name="server_rpc_port"></a><a href="#server_rpc_port">`server`</a> - Server RPC address. Default 8300.
* <a name="protocol"></a><a href="#protocol">`protocol`</a> Equivalent to the
[`-protocol` command-line flag](#_protocol).
* <a name="reap"></a><a href="#reap">`reap`</a> This controls Consul's automatic reaping of child processes,
which is useful if Consul is running as PID 1 in a Docker container. If this isn't specified, then Consul will
automatically reap child processes if it detects it is running as PID 1. If this is set to true or false, then
it controls reaping regardless of Consul's PID (forces reaping on or off, respectively).
* <a name="reconnect_timeout"></a><a href="#reconnect_timeout">`reconnect_timeout`</a> This controls
how long it takes for a failed node to be completely removed from the cluster. This defaults to
72 hours and it is recommended that this is set to at least double the maximum expected recoverable
outage time for a node or network partition. WARNING: Setting this time too low could cause Consul
servers to be removed from quorum during an extended node failure or partition, which could complicate
recovery of the cluster. The value is a time with a unit suffix, which can be "s", "m", "h" for seconds,
minutes, or hours. The value must be >= 8 hours.
* <a name="reconnect_timeout_wan"></a><a href="#reconnect_timeout_wan">`reconnect_timeout_wan`</a> This
is the WAN equivalent of the <a href="#reconnect_timeout">`reconnect_timeout`</a> parameter, which
controls how long it takes for a failed server to be completely removed from the WAN pool. This also
defaults to 72 hours, and must be >= 8 hours.
* <a name="recursor"></a><a href="#recursor">`recursor`</a> Provides a single recursor address.
This has been deprecated, and the value is appended to the [`recursors`](#recursors) list for
backwards compatibility.
* <a name="recursors"></a><a href="#recursors">`recursors`</a> This flag provides addresses of
upstream DNS servers that are used to recursively resolve queries if they are not inside the service
domain for consul. For example, a node can use Consul directly as a DNS server, and if the record is
outside of the "consul." domain, the query will be resolved upstream.
* <a name="rejoin_after_leave"></a><a href="#rejoin_after_leave">`rejoin_after_leave`</a> Equivalent
to the [`-rejoin` command-line flag](#_rejoin).
* <a name="retry_join"></a><a href="#retry_join">`retry_join`</a> Equivalent to the
[`-retry-join` command-line flag](#_retry_join). Takes a list
of addresses to attempt joining every [`retry_interval`](#_retry_interval) until at least one
[`-join`](#_join) works.
* <a name="retry_interval"></a><a href="#retry_interval">`retry_interval`</a> Equivalent to the
[`-retry-interval` command-line flag](#_retry_interval).
* <a name="retry_join_wan"></a><a href="#retry_join_wan">`retry_join_wan`</a> Equivalent to the
[`-retry-join-wan` command-line flag](#_retry_join_wan). Takes a list
of addresses to attempt joining to WAN every [`retry_interval_wan`](#_retry_interval_wan) until at least one
[`-join-wan`](#_join_wan) works.
* <a name="retry_interval_wan"></a><a href="#retry_interval_wan">`retry_interval_wan`</a> Equivalent to the
[`-retry-interval-wan` command-line flag](#_retry_interval_wan).
* <a name="server"></a><a href="#server">`server`</a> Equivalent to the
[`-server` command-line flag](#_server).
* <a name="server_name"></a><a href="#server_name">`server_name`</a> When provided, this overrides
the [`node_name`](#_node) for the TLS certificate. It can be used to ensure that the certificate
name matches the hostname we declare.
* <a name="session_ttl_min"></a><a href="#session_ttl_min">`session_ttl_min`</a>
The minimum allowed session TTL. This ensures sessions are not created with
TTL's shorter than the specified limit. It is recommended to keep this limit
at or above the default to encourage clients to send infrequent heartbeats.
Defaults to 10s.
* <a name="skip_leave_on_interrupt"></a><a
href="#skip_leave_on_interrupt">`skip_leave_on_interrupt`</a> This is
similar to [`leave_on_terminate`](#leave_on_terminate) but only affects
interrupt handling. When Consul receives an interrupt signal (such as
hitting Control-C in a terminal), Consul will gracefully leave the cluster.
Setting this to `true` disables that behavior. The default behavior for
this feature varies based on whether or not the agent is running as a
client or a server (prior to Consul 0.7 the default value was
unconditionally set to `false`). On agents in client-mode, this defaults
to `false` and for agents in server-mode, this defaults to `true`
(i.e. Ctrl-C on a server will keep the server in the cluster and therefore
quorum, and Ctrl-C on a client will gracefully leave).
* <a name="start_join"></a><a href="#start_join">`start_join`</a> An array of strings specifying addresses
of nodes to [`-join`](#_join) upon startup.
* <a name="start_join_wan"></a><a href="#start_join_wan">`start_join_wan`</a> An array of strings specifying
addresses of WAN nodes to [`-join-wan`](#_join_wan) upon startup.
* <a name="telemetry"></a><a href="#telemetry">`telemetry`</a> This is a nested object that configures where Consul
sends its runtime telemetry, and contains the following keys:
* <a name="telemetry-statsd_address"></a><a href="#telemetry-statsd_address">`statsd_address`</a> This provides the
address of a statsd instance in the format `host:port`. If provided, Consul will send various telemetry information to that instance for
aggregation. This can be used to capture runtime information. This sends UDP packets only and can be used with
statsd or statsite.
* <a name="telemetry-statsite_address"></a><a href="#telemetry-statsite_address">`statsite_address`</a> This provides
the address of a statsite instance in the format `host:port`. If provided, Consul will stream various telemetry information to that instance
for aggregation. This can be used to capture runtime information. This streams via TCP and can only be used with
statsite.
* <a name="telemetry-statsite_prefix"></a><a href="#telemetry-statsite_prefix">`statsite_prefix`</a>
The prefix used while writing all telemetry data to statsite. By default, this is set to "consul".
* <a name="telemetry-dogstatsd_addr"></a><a href="#telemetry-dogstatsd_addr">`dogstatsd_addr`</a> This provides the
address of a DogStatsD instance in the format `host:port`. DogStatsD is a protocol-compatible flavor of
statsd, with the added ability to decorate metrics with tags and event information. If provided, Consul will
send various telemetry information to that instance for aggregation. This can be used to capture runtime
information.
* <a name="telemetry-dogstatsd_tags"></a><a href="#telemetry-dogstatsd_tags">`dogstatsd_tags`</a> This provides a list of global tags
that will be added to all telemetry packets sent to DogStatsD. It is a list of strings, where each string
looks like "my_tag_name:my_tag_value".
* <a name="telemetry-disable_hostname"></a><a href="#telemetry-disable_hostname">`disable_hostname`</a>
This controls whether or not to prepend runtime telemetry with the machine's hostname, defaults to false.
* <a name="telemetry-circonus_api_token"></a><a href="#telemetry-circonus_api_token">`circonus_api_token`</a>
A valid API Token used to create/manage check. If provided, metric management is enabled.
* <a name="telemetry-circonus_api_app"></a><a href="#telemetry-circonus_api_app">`circonus_api_app`</a>
A valid app name associated with the API token. By default, this is set to "consul".
* <a name="telemetry-circonus_api_url"></a><a href="#telemetry-circonus_api_url">`circonus_api_url`</a>
The base URL to use for contacting the Circonus API. By default, this is set to "https://api.circonus.com/v2".
* <a name="telemetry-circonus_submission_interval"></a><a href="#telemetry-circonus_submission_interval">`circonus_submission_interval`</a>
The interval at which metrics are submitted to Circonus. By default, this is set to "10s" (ten seconds).
* <a name="telemetry-circonus_submission_url"></a><a href="#telemetry-circonus_submission_url">`circonus_submission_url`</a>
The `check.config.submission_url` field, of a Check API object, from a previously created HTTPTRAP check.
* <a name="telemetry-circonus_check_id"></a><a href="#telemetry-circonus_check_id">`circonus_check_id`</a>
The Check ID (not **check bundle**) from a previously created HTTPTRAP check. The numeric portion of the `check._cid` field in the Check API object.
* <a name="telemetry-circonus_check_force_metric_activation"></a><a href="#telemetry-circonus_check_force_metric_activation">`circonus_check_force_metric_activation`</a>
Force activation of metrics which already exist and are not currently active. If check management is enabled, the default behavior is to add new metrics as they are encoutered. If the metric already exists in the check, it will **not** be activated. This setting overrides that behavior. By default, this is set to "false".
* <a name="telemetry-circonus_check_instance_id"></a><a href="#telemetry-circonus_check_instance_id">`circonus_check_instance_id`</a>
Serves to uniquely identify the metrics comming from this *instance*. It can be used to maintain metric continuity with transient or ephemeral instances as they move around within an infrastructure. By default, this is set to hostname:application name (e.g. "host123:consul").
* <a name="telemetry-circonus_check_search_tag"></a><a href="#telemetry-circonus_check_search_tag">`circonus_check_search_tag`</a>
A special tag which, when coupled with the instance id, helps to narrow down the search results when neither a Submission URL or Check ID is provided. By default, this is set to service:app (e.g. "service:consul").
* <a name="telemetry-circonus_broker_id"></a><a href="#telemetry-circonus_broker_id">`circonus_broker_id`</a>
The ID of a specific Circonus Broker to use when creating a new check. The numeric portion of `broker._cid` field in a Broker API object. If metric management is enabled and neither a Submission URL nor Check ID is provided, an attempt will be made to search for an existing check using Instance ID and Search Tag. If one is not found, a new HTTPTRAP check will be created. By default, this is not used and a random Enterprise Broker is selected, or, the default Circonus Public Broker.
* <a name="telemetry-circonus_broker_search_tag"></a><a href="#telemetry-circonus_broker_search_tag">`circonus_broker_search_tag`</a>
A special tag which will be used to select a Circonus Broker when a Broker ID is not provided. The best use of this is to as a hint for which broker should be used based on *where* this particular instance is running (e.g. a specific geo location or datacenter, dc:sfo). By default, this is not used.
* <a name="statsd_addr"></a><a href="#statsd_addr">`statsd_addr`</a> Deprecated, see
the <a href="#telemetry">telemetry</a> structure
* <a name="statsite_addr"></a><a href="#statsite_addr">`statsite_addr`</a> Deprecated, see
the <a href="#telemetry">telemetry</a> structure
* <a name="statsite_prefix"></a><a href="#statsite_prefix">`statsite_prefix`</a> Deprecated, see
the <a href="#telemetry">telemetry</a> structure
* <a name="dogstatsd_addr"></a><a href="#dogstatsd_addr">`dogstatsd_addr`</a> Deprecated, see
he <a href="#telemetry">telemetry</a> structure
* <a name="dogstatsd_tags"></a><a href="#dogstatsd_tags">`dogstatsd_tags`</a> Deprecated, see
the <a href="#telemetry">telemetry</a> structure
* <a name="syslog_facility"></a><a href="#syslog_facility">`syslog_facility`</a> When
[`enable_syslog`](#enable_syslog) is provided, this controls to which
facility messages are sent. By default, `LOCAL0` will be used.
* <a name="translate_wan_addrs"</a><a href="#translate_wan_addrs">`translate_wan_addrs`</a> If
set to true, Consul will prefer a node's configured <a href="#_advertise-wan">WAN address</a>
when servicing DNS requests for a node in a remote datacenter. This allows the node to be
reached within its own datacenter using its local address, and reached from other datacenters
using its WAN address, which is useful in hybrid setups with mixed networks. This is disabled
by default.
* <a name="ui"></a><a href="#ui">`ui`</a> - Equivalent to the [`-ui`](#_ui)
command-line flag.
* <a name="ui_dir"></a><a href="#ui_dir">`ui_dir`</a> - Equivalent to the
[`-ui-dir`](#_ui_dir) command-line flag.
* <a name="unix_sockets"></a><a href="#unix_sockets">`unix_sockets`</a> - This
allows tuning the ownership and permissions of the
Unix domain socket files created by Consul. Domain sockets are only used if
the HTTP or RPC addresses are configured with the `unix://` prefix. The
following options are valid within this construct and apply globally to all
sockets created by Consul:
<br>
* `user` - The name or ID of the user who will own the socket file.
* `group` - The group ID ownership of the socket file. Note that this option
currently only supports numeric IDs.
* `mode` - The permission bits to set on the file.
<br>
It is important to note that this option may have different effects on
different operating systems. Linux generally observes socket file permissions
while many BSD variants ignore permissions on the socket file itself. It is
important to test this feature on your specific distribution. This feature is
currently not functional on Windows hosts.
* <a name="verify_incoming"></a><a href="#verify_incoming">`verify_incoming`</a> - If
set to true, Consul requires that all incoming
connections make use of TLS and that the client provides a certificate signed
by the Certificate Authority from the [`ca_file`](#ca_file). By default, this is false, and
Consul will not enforce the use of TLS or verify a client's authenticity. This
applies to both server RPC and to the HTTPS API. Note: to enable the HTTPS API, you
must define an HTTPS port via the [`ports`](#ports) configuration. By default, HTTPS
is disabled.
* <a name="verify_outgoing"></a><a href="#verify_outgoing">`verify_outgoing`</a> - If set to
true, Consul requires that all outgoing connections
make use of TLS and that the server provides a certificate that is signed by
the Certificate Authority from the [`ca_file`](#ca_file). By default, this is false, and Consul
will not make use of TLS for outgoing connections. This applies to clients and servers
as both will make outgoing connections.
* <a name="verify_server_hostname"></a><a href="#verify_server_hostname">`verify_server_hostname`</a> - If set to
true, Consul verifies for all outgoing connections that the TLS certificate presented by the servers
matches "server.<datacenter>.<domain>" hostname. This implies `verify_outgoing`.
By default, this is false, and Consul does not verify the hostname of the certificate, only
that it is signed by a trusted CA. This setting is important to prevent a compromised
client from being restarted as a server, and thus being able to perform a MITM attack
or to be added as a Raft peer. This is new in 0.5.1.
* <a name="watches"></a><a href="#watches">`watches`</a> - Watches is a list of watch
specifications which allow an external process to be automatically invoked when a
particular data view is updated. See the
[watch documentation](/docs/agent/watches.html) for more detail. Watches can be
modified when the configuration is reloaded.
## <a id="ports"></a>Ports Used
Consul requires up to 5 different ports to work properly, some on
TCP, UDP, or both protocols. Below we document the requirements for each
port.
* Server RPC (Default 8300). This is used by servers to handle incoming
requests from other agents. TCP only.
* Serf LAN (Default 8301). This is used to handle gossip in the LAN.
Required by all agents. TCP and UDP.
* Serf WAN (Default 8302). This is used by servers to gossip over the
WAN to other servers. TCP and UDP.
* CLI RPC (Default 8400). This is used by all agents to handle RPC
from the CLI. TCP only.
* HTTP API (Default 8500). This is used by clients to talk to the HTTP
API. TCP only.
* DNS Interface (Default 8600). Used to resolve DNS queries. TCP and UDP.
Consul will also make an outgoing connection to HashiCorp's servers for
Atlas-related features and to check for the availability of newer versions
of Consul. This will be a TLS-secured TCP connection to `scada.hashicorp.com:7223`.
## <a id="reloadable-configuration"></a>Reloadable Configuration
Reloading configuration does not reload all configuration items. The
items which are reloaded include:
* Log level
* Checks
* Services
* Watches
* HTTP Client Address
* Atlas Token
* Atlas Infrastructure
* Atlas Endpoint
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