»Connect Custom Proxy Integration

Any proxy can be extended to support Connect. Consul ships with a built-in proxy for a good development and out of the box experience, but understand that production users will require other proxy solutions.

A proxy must serve one or both of the following two roles: it must accept inbound connections or establish outbound connections identified as a particular service. One or both of these may be implemented depending on the case, although generally both must be supported.

»Accepting Inbound Connections

For inbound connections, the proxy must accept TLS connections on some port. The certificate served should be created by the /v1/agent/connect/ca/leaf/ API endpoint. The client certificate should be validated against the root certificates provided by the /v1/agent/connect/ca/roots endpoint. After validating the client certificate from the caller, the proxy should call the /v1/agent/connect/authorize endpoint to authorize the connection.

All of these API endpoints operate on agent-local data that is updated in the background. The leaf and roots should be updated in the background by the proxy, but the authorize endpoint is expected to be called in the connection path. The endpoints introduce only microseconds of additional latency on the connection.

The leaf and root cert endpoints support blocking queries. These should be used if possible to get near-immediate updates for root cert rotations, leaf expiry, etc.

»Establishing Outbound Connections

For outbound connections, the proxy should communicate to a Connect-capable endpoint for a service and provide a client certificate from the /v1/agent/connect/ca/leaf/ API endpoint. The certificate served by the remote endpoint can be verified against the root certificates from the /v1/agent/connect/ca/roots endpoint.

»Configuration Discovery

Any proxy can discover proxy configuration registered with a local service instance using the /v1/agent/service/:service_id API endpoint.

The discovery chain for each upstream service should be fetched from the /v1/discovery-chain/:service_id API endpoint.

For each target in the resulting discovery chain, a list of healthy endpoints can be fetched from the /v1/health/connect/:service_id API endpoint.