Health checking

• Health checking architecture overview.

• If health checking is configured for a cluster, additional statistics are emitted. They are documented here.

• v3 API documentation.

TCP health checking

The type of matching performed is the following:

tcp_health_check:
    send: {text: '0101'}
    receive: [{text: '02'}, {text: '03'}]

During each health check cycle, all of the “send” bytes are sent to the target server.

When checking the response, “fuzzy” matching is performed such that each block must be found, and in the order specified, but not necessarily contiguous. Thus, in the example above, “04” could be inserted in the response between “02” and “03” and the check would still pass. This is done to support protocols that insert non-deterministic data, such as time, into the response.

Health checks that require a more complex pattern such as send/receive/send/receive are not currently possible.

If “receive” is an empty array, Envoy will perform “connect only” TCP health checking. During each cycle, Envoy will attempt to connect to the upstream host, and consider it a success if the connection succeeds. A new connection is created for each health check cycle.