open-consul/agent/proxycfg/proxycfg.go

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// Package proxycfg provides a component that monitors local agent state for
// Connect proxy service registrations and maintains the necessary cache state
// for those proxies locally. Local cache state keeps pull based proxies (e.g.
// the built in one) performant even on first request/startup, and allows for
// push-based proxy APIs (e.g. xDS for Envoy) to be notified of updates to the
// proxy configuration.
//
// The relationship with other agent components looks like this:
//
// +------------------------------------------+
// | AGENT |
// | |
// | +--------+ 1. +----------+ |
// | | local |<-----+ proxycfg |<--------+ |
// | | state +----->| Manager |<---+ | |
// | +--------+ 2. +^---+-----+ | | |
// | 5.| | | | |
// | +----------+ | +-------+--+ |4. |
// | | +->| proxycfg | | |
// | | 3.| | State | | |
// | | | +----------+ | |
// | | | | |
// | | | +----------+ | |
// | | +->| proxycfg +-+ |
// | | | State | |
// | | +----------+ |
// | |6. |
// | +----v---+ |
// | | xDS | |
// | | Server | |
// | +--------+ |
// | |
// +------------------------------------------+
//
// 1. Manager watches local state for changes.
// 2. On local state change manager is notified and iterates through state
// looking for proxy service registrations.
// 3. For each proxy service registered, the manager maintains a State
// instance, recreating on change, removing when deregistered.
// 4. State instance copies the parts of the the proxy service registration
// needed to configure proxy, and sets up blocking watches on the local
// agent cache for all remote state needed: root and leaf certs, intentions,
// and service discovery results for the specified upstreams. This ensures
// these results are always in local cache for "pull" based proxies like the
// built-in one.
// 5. If needed, pull-based proxy config APIs like the xDS server can Watch the
// config for a given proxy service.
// 6. Watchers get notified every time something changes the current snapshot
// of config for the proxy. That might be changes to the registration,
// certificate rotations, changes to the upstreams required (needing
// different listener config), or changes to the service discovery results
// for any upstream (e.g. new instance of upstream service came up).
package proxycfg