mirror of https://github.com/hashicorp/consul
179 lines
7.1 KiB
Markdown
179 lines
7.1 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
|
|
|
|
A service definition is a script that looks like:
|
|
|
|
```javascript
|
|
{
|
|
"service": {
|
|
"name": "redis",
|
|
"tags": ["primary"],
|
|
"address": "",
|
|
"port": 8000,
|
|
"enable_tag_override": false,
|
|
"checks": [
|
|
{
|
|
"script": "/usr/local/bin/check_redis.py",
|
|
"interval": "10s"
|
|
}
|
|
]
|
|
}
|
|
}
|
|
```
|
|
|
|
A service definition must include a `name` and may optionally provide an
|
|
`id`, `tags`, `address`, `port`, `check`, and `enable_tag_override`. 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.
|
|
|
|
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 will be removed in Consul 1.1.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
The check must be of the script, HTTP, TCP or TTL type. If it is a script type,
|
|
`script` and `interval` must be provided. If it is a HTTP type, `http` and
|
|
`interval` must be provided. If it is a TCP type, `tcp` and `interval` must be
|
|
provided. If it is a TTL type, then only `ttl` must be provided. 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).
|
|
|
|
-> **Note:** Consul 0.9.3 and before require the optional check ID for a check
|
|
that is embedded in a service definition to be configured via the `CheckID`
|
|
field. Consul 1.0 accepts both `id` and `CheckID` but the latter is
|
|
deprecated and will be removed in Consul 1.1.
|
|
|
|
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 will be removed in Consul 1.1.
|
|
|
|
To configure a service, either provide it 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).
|
|
|
|
## 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": [
|
|
{
|
|
"script": "/bin/check_redis -p 6000",
|
|
"interval": "5s",
|
|
"ttl": "20s"
|
|
}
|
|
]
|
|
},
|
|
{
|
|
"id": "red1",
|
|
"name": "redis",
|
|
"tags": [
|
|
"delayed",
|
|
"secondary"
|
|
],
|
|
"address": "",
|
|
"port": 7000,
|
|
"checks": [
|
|
{
|
|
"script": "/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.
|