160 lines
6.5 KiB
Markdown
160 lines
6.5 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 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
|
|
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 that is a script looks like:
|
|
|
|
```javascript
|
|
{
|
|
"service": {
|
|
"name": "redis",
|
|
"tags": ["master"],
|
|
"address": "127.0.0.1",
|
|
"port": 8000,
|
|
"enableTagOverride": 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 `enableTagOverride`. 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 "master" or "slave" 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 slave, 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).
|
|
|
|
The `enableTagOverride` can optionally be specified to disable the anti-entropy
|
|
feature for this service. If `enableTagOverride` is set to TRUE then external
|
|
agents can update this service in the [catalog](/docs/agent/http/catalog.html) and modify the tags. Subsequent
|
|
local sync operations by this agent will ignore the updated tags. For instance: If an external agent
|
|
modified both the tags and the port for this service and `enableTagOverride`
|
|
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 `enableTagOverride` 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 `enableTagOverride` configuration and all other service
|
|
configuration items are independant of one another. Updating the tags for
|
|
the service registered on one node is independant of the same service (by name)
|
|
registered on another node. If `enableTagOverride` is not specified the default
|
|
value is false. See [anti-entropy syncs](/docs/internals/anti-entropy.html)
|
|
for more info.
|
|
|
|
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" extension to be loaded by Consul. Check definitions can
|
|
also be updated by sending a `SIGHUP` to the agent. Alternatively, the
|
|
service can be registered dynamically using the [HTTP API](/docs/agent/http.html).
|
|
|
|
## Multiple Service Definitions
|
|
|
|
Multiple services definitions can be provided at once using the `services`
|
|
(plural) key in your configuration file.
|
|
|
|
```javascript
|
|
{
|
|
"services": [
|
|
{
|
|
"id": "red0",
|
|
"name": "redis",
|
|
"tags": [
|
|
"master"
|
|
],
|
|
"address": "127.0.0.1",
|
|
"port": 6000,
|
|
"checks": [
|
|
{
|
|
"script": "/bin/check_redis -p 6000",
|
|
"interval": "5s",
|
|
"ttl": "20s"
|
|
}
|
|
]
|
|
},
|
|
{
|
|
"id": "red1",
|
|
"name": "redis",
|
|
"tags": [
|
|
"delayed",
|
|
"slave"
|
|
],
|
|
"address": "127.0.0.1",
|
|
"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.
|