Cannot detect that a tcp service in Kubernetes has no pods with golang app

4/6/2019

I have a statsd client that pushes to a kubernetes-hosted statsd service in tcp.

When I redeploy the service and update its pods on the server, the data stops flowing but I have no error on the statsd client.

Based on this thread, I have added a read detection to my golang library to see if I receive a message, but nothing.

I start the connection, send statsd packets from the client, then after I while, I scale the statsd Service down to 0 pods, but the client continues to successfully read and write from the tcp channel without errors!

When I scale the deployment back to 1, the old client does not reconnect and the client and the server continue to remain non-communicating forever.

How can I receive an error from the client when the server replicas go to 0 in the Kubernetes service?

The statsd client is a fork of https://github.com/alexcesaro/statsd

Note that we are aware that statsd is used mostly in UDP but this is a custom flavor and for several reason we need one instance of this in TCP (already have several UDP ones and they don't have this problem)

...
    c.w, err = net.DialTimeout(c.network, c.addr, 5*time.Second)
...

func (c *conn) checkTCPConnectionOpen() error {
    if c.network[:3] == "tcp" {
        one := []byte{}
        _, err := c.w.Read(one)
        return err
    }
    return nil
}

func (c *conn) flush(n int) {
    if len(c.buf) == 0 {
        return
    }
    if n == 0 {
        n = len(c.buf)
    }

    err := c.checkTCPConnectionOpen()
    c.handleError(err)

    _, err = c.w.Write(c.buf[:n])
    c.handleError(err)
    if n < len(c.buf) {
        copy(c.buf, c.buf[n:])
    }
    c.buf = c.buf[:len(c.buf)-n]
}
-- MaurGi
go
kubernetes
tcp

2 Answers

4/10/2019

Ok so this is not a Kubernetes problem, but a golang one.

This is basically a duplicate of How to know TCP connection is closed in Golang net package?

-- MaurGi
Source: StackOverflow

4/6/2019

Is there a particular reason why you want to use a TCP connection? It looks like Statsd supports UDP mode see here. It seems like your desire to achieve resilience on your Statsd client would be better served if you opt to run the server over UDP.

-- brianSan
Source: StackOverflow