61 lines
2.5 KiB
Markdown
61 lines
2.5 KiB
Markdown
---
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layout: "docs"
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page_title: "Service Definition"
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sidebar_current: "docs-agent-services"
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---
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# Services
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One of the main goals of service discovery is to provide a catalog of available
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services. To that end, the agent provides a simple service definition format
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to declare the availability of a service, and to potentially associate it with
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a health check. A health check is considered to be application level if it
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associated with a service. A service is defined in a configuration file,
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or added at runtime over the HTTP interface.
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## Service Definition
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A service definition that is a script looks like:
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{
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"service": {
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"name": "redis",
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"tags": ["master"],
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"port": 8000,
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"check": {
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"script": "/usr/local/bin/check_redis.py",
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"interval": "10s"
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}
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}
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}
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A service definition must include a `name`, and may optionally provide
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an `id`, `tags`, `port`, and `check`. The `id` is set to the `name` if not
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provided. It is required that all services have a unique ID per node, so if names
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might conflict then unique ID's should be provided.
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The `tags` is a list of opaque value to Consul, but can be used to distinguish
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between "master" or "slave" nodes, different versions, or any other service level labels.
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The `port` can be used as well to make a service oriented architecture
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simpler to configure. This way the address and port of a service can
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be discovered.
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Lastly, a service can have an associated health check. This is a powerful
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feature as it allows a web balancer to gracefully remove failing nodes, or
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a database to replace a failed slave, etc. The health check is strongly integrated
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in the DNS interface as well. If a service is failing its health check or
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a node has any failing system-level check, the DNS interface will omit that
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node from any service query.
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There is more information about [checks here](/docs/agent/checks.html). The
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check must be of the script or TTL type. If it is a script type, `script` and
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`interval` must be provided. If it is a TTL type, then only `ttl` must be
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provided. The check name is automatically generated as "service:<service-id>".
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To configure a service, either provide it as a `-config-file` option to the
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agent, or place it inside the `-config-dir` of the agent. The file must
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end in the ".json" extension to be loaded by Consul. Check definitions can
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also be updated by sending a `SIGHUP` to the agent. Alternatively, the
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service can be registered dynamically using the [HTTP API](/docs/agent/http.html).
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