2021-04-26 18:58:44 +00:00
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# Agent Configuration
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2021-07-06 23:28:00 +00:00
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The [Agent Configuration] is the primary mechanism for configuring Consul. Agent
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Configuration also allows for specifying [Config Entries], [Services], and [Checks] that
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will be loaded when the agent starts.
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Most configuration comes from [hcl] or `json` files, but some configuration can also be
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specified using command line flags, and some can be loaded with [Auto-Config].
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See also the [checklist for adding a new field] to the configuration.
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[hcl]: https://github.com/hashicorp/hcl/tree/hcl1
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[Agent Configuration]: https://www.consul.io/docs/agent/options
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[checklist for adding a new field]: ./checklist-adding-config-fields.md
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[Auto-Config]: #auto-config
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[Config Entries]: https://www.consul.io/docs/agent/options#config_entries
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[Services]: https://www.consul.io/docs/discovery/services
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[Checks]: https://www.consul.io/docs/discovery/checks
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## Code
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The Agent Configuration is implemented in [agent/config], and the primary entrypoint is
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[Load]. Config loading is performed in phases:
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1. Command line flags are used to create a `config.LoadOpts` and passed to `Load`.
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2. `Load` reads all the config files and builds an ordered list of `config.Source`.
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3. Each `config.Source` is read to produce a `config.Config`.
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4. Each `config.Config` is merged ontop the previous.
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5. A `config.RuntimeConfig` is produced from the merged `config.Config`
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6. The `config.RuntimeConfig` is validated.
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7. Finally a result is returned with the `RuntimeConfig` and any warnings, or an error.
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[agent/config]: https://github.com/hashicorp/consul/tree/main/agent/config
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[Load]: https://pkg.go.dev/github.com/hashicorp/consul/agent/config#Load
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If [Auto-Config] is enabled, when it receives the config from the server, the
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entire process is repeated a second time with the addition config provided as another
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`config.Source`.
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Default values can be specified in one of the [default sources] or set when
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converting from `Config` to `RuntimeConfig` in [builder.build]. Hopefully in the future we
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should remove one of those ways of setting default values.
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[default sources]: https://github.com/hashicorp/consul/blob/main/agent/config/default.go
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[builder.build]: https://github.com/hashicorp/consul/blob/main/agent/config/builder.go
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## Auto-Config
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Auto-Config is enabled by the [auto_config] field in an Agent Configuration file. It is
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implemented in a couple packages.
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* the server RPC endpoint is in [agent/consul/auto_config_endpoint.go]
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* the client that receives and applies the config is implemented in [agent/auto-config]
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[auto_config]: https://www.consul.io/docs/agent/options#auto_config
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[agent/consul/auto_config_endpoint.go]: https://github.com/hashicorp/consul/blob/main/agent/consul/auto_config_endpoint.go
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[agent/auto-config]: https://github.com/hashicorp/consul/tree/main/agent/auto-config
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