Stolon proxy breakes connection even when --stop-listening=false

[wildermesser]

What happened:
Recently I reproduced the issue #674. I am using slow etcd, so sometimes requests to kubernetes-apiserver exceed the limit of 10s. At this moment stolon proxy breaks connection from clients as expected. In the logs I saw check timeout timer fired; Stopping listening.
To avoid this, I add --stop-listening=false to stolon-proxy args. Now in case of slow requests, I am getting:

2022-01-13T05:13:54.881Z	INFO	cmd/proxy.go:346	check function error	{"error": "cannot get cluster data: failed to get latest version of configmap: Get \"https://10.233.0.1:443/api/v1/namespaces/ptaf-stolon/configmaps/stolon-cluster-kube-stolon?timeout=10s\": net/http: request canceled (Client.Timeout exceeded while awaiting headers)"}
2022-01-13T05:13:55.119Z	INFO	cmd/proxy.go:304	check timeout timer fired

Without message like Stopping listening. But! At this moment my python application still become connection reset:

connection was closed in the middle of operation
ConnectionResetError: [Errno 104] Connection reset by peer

What you expected to happen:
When --stop-listening=false passed as arg to stolon-proxy, connections are still alive despite store backend issues.

Environment:

• Stolon version:

stolon@stolon-proxy-779f67f5d8-smzbh:/$ stolon-proxy --version
stolon-proxy version 3bb7499f815f77140551eb762b200cf4557f57d3

• Stolon running environment: k8s 1.20.11, stolon store backend - kubernetes configmap

[sgotti]

@wildermesser This is the right behavior to maintain data consistency. If the proxy cannot know the cluster state for a specified interval it'll close connections (see https://github.com/sorintlab/stolon/blob/master/doc/faq.md#why-clients-should-use-the-stolon-proxy).

The right solutions are:

• make your store faster (see also https://github.com/sorintlab/stolon/blob/master/doc/architecture.md)
• Increase the proxy timeout.

What you expected to happen:
When --stop-listening=false passed as arg to stolon-proxy, connections are still alive despite store backend issues.

With or without --stop-listening the proxy will always close connections when it cannot detect the cluster state.
--stop-listening will only change the "listening" behavior: keep the tcp listener opened (but dropping connections) or also close it. This option is useful only for handling different load balancing behaviors.

[wildermesser]

@sgotti thank you for explaining!

[nh2]

Increase the proxy timeout.

@sgotti which setting is that? Is it --tcp-keepalive-count?

Also, what happens after check timeout timer fired + Stopping listening occurred, should the proxy ever reconnect/recover? If yes, does that depend on what --stop-listening is set to?

[nh2]

Increase the proxy timeout.

@sgotti which setting is that? Is it --tcp-keepalive-count?

Ah, it's probably proxyTimeout from the Cluster Specification.

So only the other recovery question remains.

[nh2]

Also, what happens after check timeout timer fired + Stopping listening occurred, should the proxy ever reconnect/recover?

I think I found the answer: "It should recover, but does not, due to this bug": #888 (comment)

PR to work around the issue: #907