python read_namespaced_pod_log with follow=True hangs when there is a long gap between logs from pod

What happened (please include outputs or screenshots): If I try to read the logs of a pod with the following:

from kubernetes import config, client
config.load_incluster_config()
k8s = client.CoreV1Api()
namespace = "default"
pod_name="watch-this"
logs = k8s.read_namespaced_pod_log(
    name=pod_name,
    namespace=namespace,
    follow=True,
    _preload_content=False,
)
for line in logs:
  print(line)

and there is a gap (say 5 minutes) between line1 and line2 of the log being written, then the function hangs after the first line

What you expected to happen:

the function should read all the logs as they are written from the watched pod and then exit once finished

How to reproduce it (as minimally and precisely as possible):

Create the following pod to watch:

apiVersion: v1
kind: Pod
metadata:
  name: watch-this
  namespace: default
spec:
  containers:
  - command:
    - python3
    - -u
    - -c
    - |
      from time import sleep
      for i in range(3):
        print(i)
        if i != 2:
          sleep(300)
    image: python:3.7.4-slim-stretch
    imagePullPolicy: IfNotPresent
    name: python
    resources: {}
    stdin: true
    stdinOnce: true
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
  priority: 0
  restartPolicy: Never
  schedulerName: default-scheduler
  serviceAccountName: default
  terminationGracePeriodSeconds: 30

then watch the pod with the following:

kubectl -n default run -i -t test-python-kube-client --image=python:3.7.4-slim-stretch --restart=Never --command -- /bin/sh

pip install kubernetes==11.0.0
python
from kubernetes import config, client
config.load_incluster_config()
k8s = client.CoreV1Api()
namespace = "default"
pod_name="watch-this"
logs = k8s.read_namespaced_pod_log(
    name=pod_name,
    namespace=namespace,
    follow=True,
    _preload_content=False,
)
for line in logs:
  print(line)

the output should get stuck like this: b'0\n'

however if I run the equivalent request using kubectl proxy and the kubernetes API, it works as expected:

kubectl proxy --port=8080 &
curl http://localhost:8080/api/v1/namespaces/default/pods/watch-this/log?follow=true
0
1
2

Anything else we need to know?:

Environment:

Kubernetes version (Client Version: version.Info{Major:"1", Minor:"14", GitVersion:"v1.14.1", GitCommit:"b7394102d6ef778017f2ca4046abbaa23b88c290", GitTreeState:"clean", BuildDate:"2019-04-08T17:11:31Z", GoVersion:"go1.12.1", Compiler:"gc", Platform:"darwin/amd64"} Server Version: version.Info{Major:"1", Minor:"16", GitVersion:"v1.16.13", GitCommit:"1da71a35d52fa82847fd61c3db20c4f95d283977", GitTreeState:"clean", BuildDate:"2020-07-15T21:59:26Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}):
OS ( MacOS 10.14.6):
Python version (3.7.4)
Python client version (kubernetes==11.0.0)

Aug 18 '20 13:08 0xdholleran

/assign cc @palnabarun

Aug 31 '20 16:08 roycaihw

/assign

Aug 31 '20 16:08 palnabarun

You can use the watch util to stream logs. For example: https://github.com/kubernetes-client/python-base/blob/fd322f70aa6c33782ab466afd4eaae271a27cbcb/watch/watch_test.py#L83-L85

Sep 09 '20 18:09 roycaihw

hi @roycaihw, that doesn't work either. If I try to stream the logs of the pod defined above with:

from kubernetes import config, client, watch
config.load_incluster_config()
k8s = client.CoreV1Api()
namespace = "default"
pod_name="watch-this"
w = watch.Watch()
for e in w.stream(k8s.read_namespaced_pod_log, name=pod_name, namespace=namespace):
    print(e)

This doesn't work either. It also hangs after the first line

Sep 10 '20 17:09 0xdholleran

I have faced the same problem this last week. After spending a fair amount of time investigating, I came to the conclusion the problem is with the TCP Keep Alive socket option, which urllib3 doesn't set by default. So, while running a long http request, the server doesn't get any tcp keep alive probes from the client and decides to close the connection without notifying the client, which then hangs waiting for the complete response from the server. These socket options worked for me (the times chosen are only for demonstration):

socket_options= [
    (socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1),
    (socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 5),
    (socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 30),
    (socket.IPPROTO_TCP, socket.TCP_KEEPCNT, 3)
]

Socket options should be set in the urllib3.PoolManager class here: https://github.com/kubernetes-client/python/blob/master/kubernetes/client/rest.py#L106

Another side effect of running long tcp connections can be seen in #1158 . Basically, connections used by the PoolManager are never closed and therefore are unusable for subsequently requests. This also makes the client hangs if it tries to make another request (read_namespaced_pod, for example) after a long running one. A dirty hack is to call rest_client.pool_manager.clear() after a long running request.

Sep 20 '20 15:09 raphael-bos

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If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta. /lifecycle stale

Dec 19 '20 16:12 fejta-bot

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If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta. /lifecycle rotten

Jan 18 '21 16:01 fejta-bot

Rotten issues close after 30d of inactivity. Reopen the issue with /reopen. Mark the issue as fresh with /remove-lifecycle rotten.

Send feedback to sig-contributor-experience at kubernetes/community. /close

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@fejta-bot: Closing this issue.

In response to this:

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/reopen

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Jul 03 '24 05:07 k8s-triage-robot

@k8s-triage-robot: Closing this issue, marking it as "Not Planned".

In response to this:

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This bot triages issues according to the following rules:

After 90d of inactivity, lifecycle/stale is applied

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You can:

Reopen this issue with /reopen

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Offer to help out with Issue Triage

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Oct 17 '25 10:10 k8s-ci-robot