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kubernetes - 如何退出节点脚本以“完成”kubernetes 作业

问题描述

我目前正在使用Process.exit(0)退出作为 kubernetes 作业在 docker 容器内运行的 node.js 脚本。这似乎并没有“完成”阻止 KEDA pod 自动缩放器移除 pod 的工作。

我将如何以一种被视为“完成”工作的方式退出节点脚本？

标签： kubernetesjobskeda

解决方案

I can be wrong but it seems to me this is the node+docker PID1 issue.

Please check very useful Avoid running nodejs as PID 1 under the docker image article that explains what is happening in the details.

It turns out that nodejs cannot receive signals and process them properly (if it is running with PID 1). Signal refers to SIGTERM, SIGINT and other kernel signals.

If you run nodejs as PID 1, the following code will not work at all:

process.on('SIGTERM', function onSigterm() {
  // do the cleaning job, but it wouldn't
  process.exit(0);
});

As a result, you will get a zombie process that will be forced to terminate by sigkill signal, which means that your “clean up” code will not be called at all.

Best practices recommend to avoid to run nodejs as PID 1, so running inside docker can cause unexpected behaviors.

Talking about docker, it is possible to use --init flag that

will wrap your process with a small init system that will take advantage of all kernel signals to its subprocesses and ensure that all orphaned processes are harvested.

For kubernetes you dont have such an option, however there is a trick you can try: you can use dumb-init as entrypoint in your image.

# Runs "/usr/bin/dumb-init -- /my/script --with --args"
ENTRYPOINT ["/usr/bin/dumb-init", "--"]

# or if you use --rewrite or other cli flags
# ENTRYPOINT ["dumb-init", "--rewrite", "2:3", "--"]

CMD ["/my/script", "--with", "--args"]

dumb-init is a simple process supervisor and init system designed to run as PID 1 inside minimal container environments (such as Docker). It is deployed as a small, statically-linked binary written in C.

Lightweight containers have popularized the idea of running a single process or service without normal init systems like systemd or sysvinit. However, omitting an init system often leads to incorrect handling of processes and signals, and can result in problems such as containers which can't be gracefully stopped, or leaking containers which should have been destroyed.

dumb-init enables you to simply prefix your command with dumb-init. It acts as PID 1 and immediately spawns your command as a child process, taking care to properly handle and forward signals as they are received.

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