mirror of https://github.com/hashicorp/consul
288 lines
12 KiB
Markdown
288 lines
12 KiB
Markdown
---
|
|
layout: "docs"
|
|
page_title: "Service Definition"
|
|
sidebar_current: "docs-agent-services"
|
|
description: |-
|
|
One of the main goals of service discovery is to provide a catalog of available services. To that end, the agent provides a simple service definition format to declare the availability of a service and to potentially associate it with a health check. A health check is considered to be application level if it is associated with a service. A service is defined in a configuration file or added at runtime over the HTTP interface.
|
|
---
|
|
|
|
# Services
|
|
|
|
One of the main goals of service discovery is to provide a catalog of available
|
|
services. To that end, the agent provides a simple service definition format
|
|
to declare the availability of a service and to potentially associate it with
|
|
a health check. A health check is considered to be application level if it is
|
|
associated with a service. A service is defined in a configuration file
|
|
or added at runtime over the HTTP interface.
|
|
|
|
## Service Definition
|
|
|
|
To configure a service, either provide the service definition as a
|
|
`-config-file` option to the agent or place it inside the `-config-dir` of the
|
|
agent. The file must end in the `.json` or `.hcl` extension to be loaded by
|
|
Consul. Check definitions can be updated by sending a `SIGHUP` to the agent.
|
|
Alternatively, the service can be registered dynamically using the [HTTP
|
|
API](/api/index.html).
|
|
|
|
A service definition is a configuration that looks like the following. This
|
|
example shows all possible fields, but note that only a few are required.
|
|
|
|
```javascript
|
|
{
|
|
"service": {
|
|
"id": "redis",
|
|
"name": "redis",
|
|
"tags": ["primary"],
|
|
"address": "",
|
|
"meta": {
|
|
"meta": "for my service"
|
|
},
|
|
"port": 8000,
|
|
"enable_tag_override": false,
|
|
"checks": [
|
|
{
|
|
"args": ["/usr/local/bin/check_redis.py"],
|
|
"interval": "10s"
|
|
}
|
|
],
|
|
"kind": "connect-proxy",
|
|
"proxy_destination": "redis", // Deprecated
|
|
"proxy": {
|
|
"destination_service_name": "redis",
|
|
"destination_service_id": "redis1",
|
|
"local_service_address": "127.0.0.1",
|
|
"local_service_port": 9090,
|
|
"config": {},
|
|
"upstreams": []
|
|
},
|
|
"connect": {
|
|
"native": false,
|
|
"sidecar_service": {}
|
|
"proxy": { // Deprecated
|
|
"command": [],
|
|
"config": {}
|
|
}
|
|
},
|
|
"weights": {
|
|
"passing": 5,
|
|
"warning": 1
|
|
}
|
|
}
|
|
}
|
|
```
|
|
|
|
A service definition must include a `name` and may optionally provide an
|
|
`id`, `tags`, `address`, `meta`, `port`, `enable_tag_override`, and `check`.
|
|
The `id` is set to the `name` if not provided. It is required that all
|
|
services have a unique ID per node, so if names might conflict then
|
|
unique IDs should be provided.
|
|
|
|
The `tags` property is a list of values that are opaque to Consul but
|
|
can be used to distinguish between `primary` or `secondary` nodes,
|
|
different versions, or any other service level labels.
|
|
|
|
The `address` field can be used to specify a service-specific IP address. By
|
|
default, the IP address of the agent is used, and this does not need to be provided.
|
|
The `port` field can be used as well to make a service-oriented architecture
|
|
simpler to configure; this way, the address and port of a service can
|
|
be discovered.
|
|
|
|
The `meta` object is a map of max 64 key/values with string semantics. Key can contain
|
|
only ASCII chars and no special characters (`A-Z` `a-z` `0-9` `_` and `-`).
|
|
For performance and security reasons, values as well as keys are limited to 128
|
|
characters for keys, 512 for values. This object has the same limitations as the node
|
|
meta object in node definition.
|
|
All those meta data can be retrieved individually per instance of the service
|
|
and all the instances of a given service have their own copy of it.
|
|
|
|
Services may also contain a `token` field to provide an ACL token. This token is
|
|
used for any interaction with the catalog for the service, including
|
|
[anti-entropy syncs](/docs/internals/anti-entropy.html) and deregistration.
|
|
|
|
The `enable_tag_override` can optionally be specified to disable the
|
|
anti-entropy feature for this service. If `enable_tag_override` is set to
|
|
`TRUE` then external agents can update this service in the
|
|
[catalog](/api/catalog.html) and modify the tags. Subsequent
|
|
local sync operations by this agent will ignore the updated tags. For
|
|
example, if an external agent modified both the tags and the port for
|
|
this service and `enable_tag_override` was set to `TRUE` then after the next
|
|
sync cycle the service's port would revert to the original value but the
|
|
tags would maintain the updated value. As a counter example: If an
|
|
external agent modified both the tags and port for this service and
|
|
`enable_tag_override` was set to `FALSE` then after the next sync cycle the
|
|
service's port *and* the tags would revert to the original value and all
|
|
modifications would be lost.
|
|
|
|
It's important to note that this applies only to the locally registered
|
|
service. If you have multiple nodes all registering the same service
|
|
their `enable_tag_override` configuration and all other service
|
|
configuration items are independent of one another. Updating the tags
|
|
for the service registered on one node is independent of the same
|
|
service (by name) registered on another node. If `enable_tag_override` is
|
|
not specified the default value is false. See [anti-entropy
|
|
syncs](/docs/internals/anti-entropy.html) for more info.
|
|
|
|
For Consul 0.9.3 and earlier you need to use `enableTagOverride`. Consul 1.0
|
|
supports both `enable_tag_override` and `enableTagOverride` but the latter is
|
|
deprecated and has been removed as of Consul 1.1.
|
|
|
|
### Connect
|
|
|
|
The `kind` field is used to optionally identify the service as a [Connect
|
|
proxy](/docs/connect/proxies.html) instance with the value `connect-proxy`. For
|
|
typical non-proxy instances the `kind` field must be omitted. The `proxy` field
|
|
is also required for Connect proxy registrations and is only valid if `kind` is
|
|
`connect-proxy`. The only required `proxy` field is `destination_service_name`.
|
|
For more detail please see [complete proxy configuration
|
|
example](/docs/connect/proxies.html#complete-configuration-example)
|
|
|
|
-> **Deprecation Notice:** From version 1.2.0 to 1.3.0, proxy destination was
|
|
specified using `proxy_destination` at the top level. This will continue to work
|
|
until at least 1.5.0 but it's highly recommended to switch to using
|
|
`proxy.destination_service_name`.
|
|
|
|
The `connect` field can be specified to configure
|
|
[Connect](/docs/connect/index.html) for a service. This field is available in
|
|
Consul 1.2.0 and later. The `native` value can be set to true to advertise the
|
|
service as [Connect-native](/docs/connect/native.html). The `sidecar_service`
|
|
field is an optional nested service definition its behavior and defaults are
|
|
described in [Sidecar Service
|
|
Registration](/docs/connect/proxies/sidecar-service.html). If `native` is true,
|
|
it is an error to also specify a sidecar service registration.
|
|
|
|
-> **Deprecation Notice:** From version 1.2.0 to 1.3.0 during beta, Connect
|
|
supported "Managed" proxies which are specified with the `connect.proxy` field.
|
|
[Managed Proxies are deprecated](/docs/connect/proxies/managed-deprecated.html)
|
|
and the `connect.proxy` field will be removed in a future major release.
|
|
|
|
### Checks
|
|
|
|
A service can have an associated health check. This is a powerful feature as
|
|
it allows a web balancer to gracefully remove failing nodes, a database
|
|
to replace a failed secondary, etc. The health check is strongly integrated in
|
|
the DNS interface as well. If a service is failing its health check or a
|
|
node has any failing system-level check, the DNS interface will omit that
|
|
node from any service query.
|
|
|
|
There are several check types that have differing required options as
|
|
[documented here](/docs/agent/checks.html). The check name is automatically
|
|
generated as `service:<service-id>`. If there are multiple service checks
|
|
registered, the ID will be generated as `service:<service-id>:<num>` where
|
|
`<num>` is an incrementing number starting from `1`.
|
|
|
|
-> **Note:** There is more information about [checks here](/docs/agent/checks.html).
|
|
|
|
### DNS SRV Weights
|
|
|
|
The `weights` field is an optional field to specify the weight of a service in
|
|
DNS SRV responses. If this field is not specified, its default value is:
|
|
`"weights": {"passing": 1, "warning": 1}`. When a service is `critical`, it is
|
|
excluded from DNS responses. Services with warning checks are included in
|
|
responses by default, but excluded if the optional param `only_passing = true`
|
|
is present in agent DNS configuration or `?passing` is used via the API.
|
|
|
|
When DNS SRV requests are made, the response will include the weights specified
|
|
given the state of the service. This allows some instances to be given higher
|
|
weight if they have more capacity, and optionally allows reducing load on
|
|
services with checks in `warning` status by giving passing instances a higher
|
|
weight.
|
|
|
|
### Enable Tag Override and Anti-Entropy
|
|
|
|
Services may also contain a `token` field to provide an ACL token. This token is
|
|
used for any interaction with the catalog for the service, including
|
|
[anti-entropy syncs](/docs/internals/anti-entropy.html) and deregistration.
|
|
|
|
You can optionally disable the anti-entropy feature for this service using the
|
|
`enable_tag_override` flag. External agents can modify tags on services in the
|
|
catalog, so subsequent sync operations can either maintain tag modifications or
|
|
revert them. If `enable_tag_override` is set to `TRUE`, the next sync cycle may
|
|
revert some service properties, **but** the tags would maintain the updated value.
|
|
If `enable_tag_override` is set to `FALSE`, the next sync cycle will revert any
|
|
updated service properties, **including** tags, to their original value.
|
|
|
|
It's important to note that this applies only to the locally registered
|
|
service. If you have multiple nodes all registering the same service
|
|
their `enable_tag_override` configuration and all other service
|
|
configuration items are independent of one another. Updating the tags
|
|
for the service registered on one node is independent of the same
|
|
service (by name) registered on another node. If `enable_tag_override` is
|
|
not specified the default value is false. See [anti-entropy
|
|
syncs](/docs/internals/anti-entropy.html) for more info.
|
|
|
|
For Consul 0.9.3 and earlier you need to use `enableTagOverride`. Consul 1.0
|
|
supports both `enable_tag_override` and `enableTagOverride` but the latter is
|
|
deprecated and has been removed as of Consul 1.1.
|
|
|
|
## Multiple Service Definitions
|
|
|
|
Multiple services definitions can be provided at once using the plural
|
|
`services` key in your configuration file.
|
|
|
|
```javascript
|
|
{
|
|
"services": [
|
|
{
|
|
"id": "red0",
|
|
"name": "redis",
|
|
"tags": [
|
|
"primary"
|
|
],
|
|
"address": "",
|
|
"port": 6000,
|
|
"checks": [
|
|
{
|
|
"args": ["/bin/check_redis", "-p", "6000"],
|
|
"interval": "5s",
|
|
"ttl": "20s"
|
|
}
|
|
]
|
|
},
|
|
{
|
|
"id": "red1",
|
|
"name": "redis",
|
|
"tags": [
|
|
"delayed",
|
|
"secondary"
|
|
],
|
|
"address": "",
|
|
"port": 7000,
|
|
"checks": [
|
|
{
|
|
"args": ["/bin/check_redis", "-p", "7000"],
|
|
"interval": "30s",
|
|
"ttl": "60s"
|
|
}
|
|
]
|
|
},
|
|
...
|
|
]
|
|
}
|
|
```
|
|
|
|
## Service and Tag Names with DNS
|
|
|
|
Consul exposes service definitions and tags over the [DNS](/docs/agent/dns.html)
|
|
interface. DNS queries have a strict set of allowed characters and a
|
|
well-defined format that Consul cannot override. While it is possible to
|
|
register services or tags with names that don't match the conventions, those
|
|
services and tags will not be discoverable via the DNS interface. It is
|
|
recommended to always use DNS-compliant service and tag names.
|
|
|
|
DNS-compliant service and tag names may contain any alpha-numeric characters, as
|
|
well as dashes. Dots are not supported because Consul internally uses them to
|
|
delimit service tags.
|
|
|
|
## Service Definition Parameter Case
|
|
|
|
For historical reasons Consul's API uses `CamelCased` parameter names in
|
|
responses, however it's configuration file uses `snake_case` for both HCL and
|
|
JSON representations. For this reason the registration _HTTP APIs_ accept both
|
|
name styles for service definition parameters although APIs will return the
|
|
listings using `CamelCase`.
|
|
|
|
Note though that **all config file formats require
|
|
`snake_case` fields**. We always document service definition examples using
|
|
`snake_case` and JSON since this format works in both config files and API
|
|
calls.
|