Listener discovery service¶
The listener discovery service (LDS) is an optional API that Envoy will call to dynamically fetch listeners. Envoy will reconcile the API response and add, modify, or remove known listeners depending on what is required.
The semantics of listener updates are as follows:
- Every listener must have a unique name. If a name is not provided, Envoy will create a UUID. Listeners that are to be dynamically updated should have a unique name supplied by the management server.
- When a listener is added, it will be “warmed” before taking traffic. For example, if the listener references an RDS configuration, that configuration will be resolved and fetched before the listener is moved to “active.”
- Listeners are effectively constant once created. Thus, when a listener is updated, an entirely new listener is created (with the same listen socket). This listener goes through the same warming process described above for a newly added listener.
- When a listener is updated or removed, the old listener will be placed into a “draining” state
much like when the entire server is drained for restart. Connections owned by the listener will
be gracefully closed (if possible) for some period of time before the listener is removed and any
remaining connections are closed. The drain time is set via the
--drain-time-soption.
{
"cluster": "...",
"refresh_delay_ms": "..."
}
- cluster
- (required, string) The name of an upstream cluster that hosts the listener discovery service. The cluster must run a REST service that implements the LDS HTTP API. NOTE: This is the name of a cluster defined in the cluster manager configuration, not the full definition of a cluster as in the case of SDS and CDS.
- refresh_delay_ms
- (optional, integer) The delay, in milliseconds, between fetches to the LDS API. Envoy will add an additional random jitter to the delay that is between zero and refresh_delay_ms milliseconds. Thus the longest possible refresh delay is 2 * refresh_delay_ms. Default value is 30000ms (30 seconds).
REST API¶
-
GET/v1/listeners/(string: service_cluster)/(string: service_node)¶
Asks the discovery service to return all listeners for a particular service_cluster and
service_node. service_cluster corresponds to the --service-cluster CLI option.
service_node corresponds to the --service-node CLI option. Responses use the following
JSON schema:
{
"listeners": []
}
- listeners
- (Required, array) A list of listeners that will be dynamically added/modified within the listener manager. The management server is expected to respond with the complete set of listeners that Envoy should configure during each polling cycle. Envoy will reconcile this list with the listeners that are currently loaded and either add/modify/remove listeners as necessary.
Statistics¶
LDS has a statistics tree rooted at listener_manager.lds. with the following statistics:
| Name | Type | Description |
|---|---|---|
| config_reload | Counter | Total API fetches that resulted in a config reload due to a different config |
| update_attempt | Counter | Total API fetches attempted |
| update_success | Counter | Total API fetches completed successfully |
| update_failure | Counter | Total API fetches that failed (either network or schema errors) |
| version | Gauge | Hash of the contents from the last successful API fetch |