Prior to #13244, connect proxies and gateways could only be configured by an
xDS session served by the local client agent.
In an upcoming release, it will be possible to deploy a Consul service mesh
without client agents. In this model, xDS sessions will be handled by the
servers themselves, which necessitates load-balancing to prevent a single
server from receiving a disproportionate amount of load and becoming
overwhelmed.
This introduces a simple form of load-balancing where Consul will attempt to
achieve an even spread of load (xDS sessions) between all healthy servers.
It does so by implementing a concurrent session limiter (limiter.SessionLimiter)
and adjusting the limit according to autopilot state and proxy service
registrations in the catalog.
If a server is already over capacity (i.e. the session limit is lowered),
Consul will begin draining sessions to rebalance the load. This will result
in the client receiving a `RESOURCE_EXHAUSTED` status code. It is the client's
responsibility to observe this response and reconnect to a different server.
Users of the gRPC client connection brokered by the
consul-server-connection-manager library will get this for free.
The rate at which Consul will drain sessions to rebalance load is scaled
dynamically based on the number of proxies in the catalog.
The name of the metric as registered with the metrics library to provide
the help string, was incorrect compared with the actual code that sets
the metric value - bring them into sync.
Also, the help message was incorrect. Rather than copy the help message
from telemetry.mdx, which was correct, but felt a bit unnatural in the
way it was worded, update both of them to a new wording.
Add changelog to document what changed.
Add entry to telemetry section of the website to document what changed
Add docs to the usagemetric endpoint to help document the metrics in code
This PR adds cluster members to the metrics API. The number of members per
segment are reported as well as the total number of members.
Tested by running a multi-node cluster locally and ensuring the numbers were
correct. Also added unit test coverage to add the new expected gauges to
existing test cases.
Previously, we would emit service usage metrics both with and without a
namespace label attached. This is problematic in the case when you want
to aggregate metrics together, i.e. "sum(consul.state.services)". This
would cause services to be counted twice in that aggregate, once via the
metric emitted with a namespace label, and once in the metric emited
without any namespace label.
Using the newly provided state store methods, we periodically emit usage
metrics from the servers.
We decided to emit these metrics from all servers, not just the leader,
because that means we do not have to care about leader election flapping
causing metrics turbulence, and it seems reasonable for each server to
emit its own view of the state, even if they should always converge
rapidly.
Dan Upton