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https://issues.apache.org/jira/browse/KAFKA-2426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15113338#comment-15113338
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Alex Loddengaard commented on KAFKA-2426:
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Hi [~mcluseau], I've been looking into this and I'm having trouble
understanding what's going on.
For one, my understanding of docker networking is when
`--userland-proxy=false`, iptables will DNAT with hairpinning. If my
understanding is correct, given you're using iptables, I'm surprised the
connection times out. It's possible kubernetes is changing this behavior
because kubernetes has the concept of a "pod IP" and creates a separate
container for the pod network namespace. But the documentation doesn't dive any
deeper, so I'm not sure.
It would be helpful if you could share your topology and explain how I can
reproduce the problem. Also, does this problem happen with raw docker? Or just
with kubernetes?
Lastly, FWIW, in most cases, a Kafka broker won't connect to itself. However,
the controller will connect to itself using the advertised hostname.
> A Kafka node tries to connect to itself through its advertised hostname
> -----------------------------------------------------------------------
>
> Key: KAFKA-2426
> URL: https://issues.apache.org/jira/browse/KAFKA-2426
> Project: Kafka
> Issue Type: Bug
> Components: network
> Affects Versions: 0.8.2.1
> Environment: Docker https://github.com/wurstmeister/kafka-docker,
> managed by a Kubernetes cluster, with an "iptables proxy".
> Reporter: Mikaël Cluseau
> Assignee: Jun Rao
>
> Hi,
> when used behind a firewall, Apache Kafka nodes are trying to connect to
> themselves using their advertised hostnames. This means that if you have a
> service IP managed by the docker's host using *only* iptables DNAT rules, the
> node's connection to "itself" times out.
> This is the case in any setup where a host will DNAT the service IP to the
> instance's IP, and send the packet back on the same interface other a Linux
> Bridge port not configured in "hairpin" mode. It's because of this:
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/bridge/br_forward.c#n30
> The specific part of the kubernetes issue is here:
> https://github.com/BenTheElder/kubernetes/issues/3#issuecomment-123925060 .
> The timeout involves that the even if partition's leader is elected, it then
> fails to accept writes from the other members, causing a write lock. and
> generating very heavy logs (as fast as Kafka usualy is, but through log4j
> this time ;)).
> This also means that the normal docker case work by going through the
> userspace-proxy, which necessarily impacts the performance.
> The workaround for us was to add a "127.0.0.2 advertised-hostname" to
> /etc/hosts in the container startup script.
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