26 lines
2.5 KiB
Markdown
26 lines
2.5 KiB
Markdown
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# Configuration Entries
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## Merging Service Config
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Merging data from defaults in config entries is roughly a two-step process:
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1. Flatten central configuration for proxies at a Consul server. Resolving config is done on behalf of a specific service, and this merge considers multiple config entries, such as proxy-defaults and service-defaults.
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2. Merge flattened central defaults into sidecar proxy registrations. This occurs at a client agent in the agentful case, or on a server in the agentless case.
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Any time the centralized defaults are updated, internal watches will fire and their data will be merged into the registration for the given sidecar proxy. You can ensure that a config entry has applied by querying the service:
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* Agentful: `/v1/agent/service/:service_id`
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* Agentless: `/v1/health/connect/:service_name?merge-central-config`
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### Agentless
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The agentless flow relies on [configentry.MergeNodeServiceWithCentralConfig](https://github.com/hashicorp/consul/blob/0402fd23a349513d3e8d137ddbffcdefcc89838b/agent/configentry/merge_service_config.go) to merge default configuration. This helper is called both when bootstrapping a new dataplane proxy and when an Envoy proxy first dials the `xds` server on a Consul server.
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This merge does not directly update the proxy registration in the catalog. The merged proxy registration is passed to the consuming `proxycfg` package.
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### Agentful
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The [agent.ServiceManager](https://github.com/hashicorp/consul/blob/0402fd23a349513d3e8d137ddbffcdefcc89838b/agent/service_manager.go#LL18) is responsible for ensuring that central configuration is merged down into proxy registrations on **client agents**. Any time a proxy is registered or updated, the service manager will set up a watch through the agent cache to fetch the central configuration.
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When the central configuration is fetched, the configuration is merged and persisted to the agent state in [serviceConfigWatch.handleUpdate](https://github.com/hashicorp/consul/blob/0402fd23a349513d3e8d137ddbffcdefcc89838b/agent/service_manager.go#L256).
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## Consuming Central Config
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Once centralized defaults have been merged into service registrations, the data becomes available to consume by the `proxycfg` package. This package assembles the necessary Consul data to generate Envoy configuration for a given proxy.
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The `proxycfg` package does not need explicit watches for the service or proxy-defaults that apply to a sidecar proxy because of how these defaults are merged into proxy registrations. When defaults change, a fresh `proxycfg` snapshot is built based on the latest registration.
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