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Posted to commits@airflow.apache.org by "YahelyUshpiz (via GitHub)" <gi...@apache.org> on 2025/12/02 10:05:46 UTC
[PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
YahelyUshpiz opened a new pull request, #58931:
URL: https://github.com/apache/airflow/pull/58931
The [extract_xcom_kill] method previously used to identify and kill the sidecar process. However, the implementation in some Alpine/BusyBox versions does not support the flag, causing the command to fail and the sidecar to hang indefinitely. This commit replaces the command with a portable shell loop that iterates over to identify processes owned by the current user. This ensures compatibility with all Alpine versions and removes the dependency on .
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---
Bug Report: KubernetesPodOperator XCom Sidecar Hangs due to pgrep missing -u option
Title
KubernetesPodOperator XCom sidecar hangs indefinitely because "pgrep -u" is not supported in some Alpine versions
Description
The KubernetesPodOperator injects a sidecar container to capture XCom values. Once the main container completes, Airflow attempts to terminate this sidecar to allow the Pod to complete.
The termination logic in PodManager.extract_xcom_kill executes the following command inside the sidecar:
kill -2 $(pgrep -u $(id -u) -f 'sh')
This command relies on pgrep supporting the -u (user) flag to filter processes by the current user. However, many lightweight container images used for sidecars (like alpine) use BusyBox's implementation of pgrep. Some versions of BusyBox pgrep do not support the -u flag, causing the command to fail with an invalid option error.
As a result:
The kill command fails.
The sidecar container continues running (executing its infinite sleep loop).
The Pod remains in the Running phase.
The Airflow task eventually times out despite the main work completing successfully.
Impact:
Task Hangs: Tasks that successfully finish their work will hang until the operator times out and causing task to fail.
False Failures: Successful tasks are marked as failed due to timeout.
**^ Add meaningful description above**
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "potiuk (via GitHub)" <gi...@apache.org>.
potiuk commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3623154233
I think this script should generally follow the original script with `-u` and fallback to alpine way if it fails, or detect busybox/alpine and use alpine-specific way. going through all processes in /proc in bash might take a long time potentially
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-4041782464
Hi maintainer, this PR was merged without a milestone set.
We've automatically set the milestone to **[Airflow 3.1.9](https://github.com/apache/airflow/milestone/134)** based on: backport label targeting v3-1-test
If this milestone is not correct, please update it to the appropriate milestone.
> This comment was generated by [Milestone Tag Assistant](https://github.com/apache/airflow/blob/main/.github/workflows/milestone-tag-assistant.yml).
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "YahelyUshpiz (via GitHub)" <gi...@apache.org>.
YahelyUshpiz commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3707094478
I agree, I'll convert to it into exception and try/catch.
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "YahelyUshpiz (via GitHub)" <gi...@apache.org>.
YahelyUshpiz commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3765351963
> Still failing
Fixed
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "potiuk (via GitHub)" <gi...@apache.org>.
potiuk merged PR #58931:
URL: https://github.com/apache/airflow/pull/58931
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "jscheffl (via GitHub)" <gi...@apache.org>.
jscheffl commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3855800405
> > I am not sure.
> > Have you considered the option to update the Alpine image? Why should we support an older version if there is a new out? This is already ~3 years old...
>
> Upgrading the image does solve the issue in this case, but since there isn’t a compatibility matrix for the XCom sidecar and users can specify any version, it might be better to implement a generic fallback. Having the user manually configure the kill command could add unnecessary friction to the user experience.
For me this is not fully convincing. If you assume somebody is updating providers to have this convenience why not expecting to also update Alpine image? Is there a reason to use the 3y old image?
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "eladkal (via GitHub)" <gi...@apache.org>.
eladkal commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-4041875859
This is provider only.
No backport needed
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "potiuk (via GitHub)" <gi...@apache.org>.
potiuk commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-4041777050
> > > I am not sure.
> > > Have you considered the option to update the Alpine image? Why should we support an older version if there is a new out? This is already ~3 years old...
> >
> >
> > Upgrading the image does solve the issue in this case, but since there isn’t a compatibility matrix for the XCom sidecar and users can specify any version, it might be better to implement a generic fallback. Having the user manually configure the kill command could add unnecessary friction to the user experience.
>
> For me this is not fully convincing. If you assume somebody is updating providers to have this convenience why not expecting to also update Alpine image? Is there a reason to use the 3y old image?
I am fine with it - as long as it is fallback
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "jscheffl (via GitHub)" <gi...@apache.org>.
jscheffl commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3765764521
One general question: You say "some Alpine versions" - do you know which? Is it then in general rather advisable to prevent usage of these versions?
On the other hand if you know this is happening in your environment, ist this then not for all Pods? Should the kill command for this case maybe made configurable that you can override it in your environment and it is in general configurable (e.g. on the default kubernetes connection like the Alpine image?
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-4041784791
### Backport successfully created: v3-1-test
Note: As of [Merging PRs targeted for Airflow 3.X](https://github.com/apache/airflow/blob/main/dev/README_AIRFLOW3_DEV.md#merging-prs-targeted-for-airflow-3x)
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.
In matter of doubt please ask in [#release-management](https://apache-airflow.slack.com/archives/C03G9H97MM2) Slack channel.
<table>
<tr>
<th>Status</th>
<th>Branch</th>
<th>Result</th>
</tr>
<tr>
<td>✅</td>
<td>v3-1-test</td>
<td><a href="https://github.com/apache/airflow/pull/63379"><img src="https://img.shields.io/badge/PR-63379-blue" alt="PR Link"></a></td>
</tr>
</table>
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "potiuk (via GitHub)" <gi...@apache.org>.
potiuk commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3719267975
Still failing
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "Nataneljpwd (via GitHub)" <gi...@apache.org>.
Nataneljpwd commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3707075451
Maybe it is also worth to add a test so that we can avoid regression in the future
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "YahelyUshpiz (via GitHub)" <gi...@apache.org>.
YahelyUshpiz commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3798398770
> I am not sure.
>
> Have you considered the option to update the Alpine image? Why should we support an older version if there is a new out? This is already ~3 years old...
Upgrading the image does solve the issue in this case, but since there isn’t a compatibility matrix for the XCom sidecar and users can specify any version, it might be better to implement a generic fallback. Having the user manually configure the kill command could add unnecessary friction to the user experience.
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "boring-cyborg[bot] (via GitHub)" <gi...@apache.org>.
boring-cyborg[bot] commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-4041777717
Awesome work, congrats on your first merged pull request! You are invited to check our [Issue Tracker](https://github.com/apache/airflow/issues) for additional contributions.
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "Nataneljpwd (via GitHub)" <gi...@apache.org>.
Nataneljpwd commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3866506713
Maybe a good idea might be to add a compatibility matrix in the docs?
I think it can also aid in solving the issue
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "Nataneljpwd (via GitHub)" <gi...@apache.org>.
Nataneljpwd commented on code in PR #58931:
URL: https://github.com/apache/airflow/pull/58931#discussion_r2658935734
##########
providers/cncf/kubernetes/src/airflow/providers/cncf/kubernetes/utils/pod_manager.py:
##########
@@ -907,27 +907,39 @@ def extract_xcom_kill(self, pod: V1Pod):
_preload_content=False,
)
) as resp:
- self._exec_pod_command(resp, "kill -2 $(pgrep -u $(id -u) -f 'sh')")
-
- def _exec_pod_command(self, resp, command: str) -> str | None:
+ xcom_kill_command = "kill -2 $(pgrep -u $(id -u) -f 'sh')"
+ # fallback command for containers that don't support pgrep -u
+ fallback_xcom_kill_command = (
+ "for f in /proc/[0-9]*/comm; do "
+ "[ -O $f ] && read c < $f && [ \"$c\" = \"sh\" ] && pid=${f%/comm} && kill -2 ${pid##*/}; "
+ "done"
+ )
+ result, error = self._exec_pod_command(resp, xcom_kill_command)
+
+ if error:
+ self.log.info("Primary kill command failed, trying fallback command")
Review Comment:
More of a warning rather than an info in my opinion
##########
providers/cncf/kubernetes/src/airflow/providers/cncf/kubernetes/utils/pod_manager.py:
##########
@@ -907,27 +907,39 @@ def extract_xcom_kill(self, pod: V1Pod):
_preload_content=False,
)
) as resp:
- self._exec_pod_command(resp, "kill -2 $(pgrep -u $(id -u) -f 'sh')")
-
- def _exec_pod_command(self, resp, command: str) -> str | None:
+ xcom_kill_command = "kill -2 $(pgrep -u $(id -u) -f 'sh')"
+ # fallback command for containers that don't support pgrep -u
+ fallback_xcom_kill_command = (
+ "for f in /proc/[0-9]*/comm; do "
+ "[ -O $f ] && read c < $f && [ \"$c\" = \"sh\" ] && pid=${f%/comm} && kill -2 ${pid##*/}; "
+ "done"
+ )
+ result, error = self._exec_pod_command(resp, xcom_kill_command)
+
+ if error:
+ self.log.info("Primary kill command failed, trying fallback command")
+ self._exec_pod_command(resp, fallback_xcom_kill_command)
+
+ def _exec_pod_command(self, resp, command: str) -> tuple[str | None, str | None]:
Review Comment:
Why add another return param instead of throwing an exception on error?
##########
providers/cncf/kubernetes/src/airflow/providers/cncf/kubernetes/utils/pod_manager.py:
##########
@@ -907,27 +907,39 @@ def extract_xcom_kill(self, pod: V1Pod):
_preload_content=False,
)
) as resp:
- self._exec_pod_command(resp, "kill -2 $(pgrep -u $(id -u) -f 'sh')")
-
- def _exec_pod_command(self, resp, command: str) -> str | None:
+ xcom_kill_command = "kill -2 $(pgrep -u $(id -u) -f 'sh')"
+ # fallback command for containers that don't support pgrep -u
+ fallback_xcom_kill_command = (
+ "for f in /proc/[0-9]*/comm; do "
+ "[ -O $f ] && read c < $f && [ \"$c\" = \"sh\" ] && pid=${f%/comm} && kill -2 ${pid##*/}; "
+ "done"
+ )
+ result, error = self._exec_pod_command(resp, xcom_kill_command)
+
+ if error:
+ self.log.info("Primary kill command failed, trying fallback command")
+ self._exec_pod_command(resp, fallback_xcom_kill_command)
+
+ def _exec_pod_command(self, resp, command: str) -> tuple[str | None, str | None]:
+ """Execute a command in the pod and return the result and error (result, error)."""
res = ""
+ error_res = ""
if not resp.is_open():
- return None
+ return None, None
self.log.info("Running command... %s", command)
resp.write_stdin(f"{command}\n")
while resp.is_open():
resp.update(timeout=1)
while resp.peek_stdout():
res += resp.read_stdout()
- error_res = ""
while resp.peek_stderr():
error_res += resp.read_stderr()
if error_res:
self.log.info("stderr from command: %s", error_res)
break
if res:
- return res
- return None
+ return res, error_res or None
Review Comment:
You might not need to convert to None here as "" will evaluate to false
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "YahelyUshpiz (via GitHub)" <gi...@apache.org>.
YahelyUshpiz commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3767246620
> One general question: You say "some Alpine versions" - do you know which? Is it then in general rather advisable to prevent usage of these versions? On the other hand if you know this is happening in your environment, ist this then not for all Pods? Should the kill command for this case maybe made configurable that you can override it in your environment and it is in general configurable (e.g. on the default kubernetes connection like the Alpine image?
On Alpine versions older than 3.14 the "-u" flag in "pgrep" doesn't exist, and it happened because the xcom sidecar image was specifically set to this version.
It is an old version, and I agree that the solution may be just to upgrade the xcom sidecar image, but im my opinion if Airflow gives the user the option to set the xcom sidecar image - a better user experience would be to handle this fallback inside Airflow instead of handing it to the client.
Also, this solution gives the most generic fallback (deleting the actual proc files), and is suitable if more cases similar to this will happen in the future.
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "jscheffl (via GitHub)" <gi...@apache.org>.
jscheffl commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3797288369
I am not sure.
Have you considered the option to update the Alpine image? Why should we support an older version if there is a new out? This is already ~3 years old...
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Re: [PR] Fix KubernetesPodOperator XCom sidecar hang on Alpine [airflow]
Posted by "boring-cyborg[bot] (via GitHub)" <gi...@apache.org>.
boring-cyborg[bot] commented on PR #58931:
URL: https://github.com/apache/airflow/pull/58931#issuecomment-3601220174
Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst)
Here are some useful points:
- Pay attention to the quality of your code (ruff, mypy and type annotations). Our [prek-hooks]( https://github.com/apache/airflow/blob/main/contributing-docs/08_static_code_checks.rst#prerequisites-for-prek-hooks) will help you with that.
- In case of a new feature add useful documentation (in docstrings or in `docs/` directory). Adding a new operator? Check this short [guide](https://github.com/apache/airflow/blob/main/airflow-core/docs/howto/custom-operator.rst) Consider adding an example DAG that shows how users should use it.
- Consider using [Breeze environment](https://github.com/apache/airflow/blob/main/dev/breeze/doc/README.rst) for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
- Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
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