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Fix preStop behavior for KEDA scale-down #2625

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Fix preStop behavior for KEDA scale-down #2625

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c294814
Fix preStop behavior for KEDA scale-down
kool79 Apr 21, 2026
9f90be0
Update pod termination process for Selenium Grid
kool79 Apr 21, 2026
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10 changes: 5 additions & 5 deletions website_and_docs/content/blog/2022/scaling-grid-with-keda.md
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Original file line number Diff line number Diff line change
Expand Up @@ -118,7 +118,7 @@ spec:
lifecycle:
preStop:
exec:
command: ["/bin/sh", "-c", "curl --request POST 'localhost:5555/se/grid/node/drain' --header 'X-REGISTRATION-SECRET;'; tail --pid=$(pgrep -f '[n]ode --bind-host false --config /opt/selenium/config.toml') -f /dev/null; sleep 30s"]
command: ["/bin/sh", "-c", "curl --request POST 'localhost:5555/se/grid/node/drain' --header 'X-REGISTRATION-SECRET;'; while curl -fs localhost:5555/status >/dev/null; do sleep 1; done; sleep 10"]
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```

#### Breaking this down
Expand All @@ -132,8 +132,8 @@ grace period for your cluster nodes as well.
- We curl the `localhost` of our pod to tell it to drain. The pod will no
longer accept new session requests and will finish its current test. More
information on this [can be found in the Selenium Grid documentation](https://www.selenium.dev/documentation/grid/advanced_features/endpoints/#drain).
- We then tail the internal node process that will continue to run until the node has been drained.
- After this we give the pod 30 seconds to finish anything else before giving the full termination command.
- Poll the Selenium node /status endpoint and wait until it becomes unavailable, indicating that the node has been fully drained and terminated.
- After this we give the pod 10 seconds to finish anything else before giving the full termination command.

And with that our application can now safely scale down our selenium browser deployments!

Expand Down Expand Up @@ -216,7 +216,7 @@ spec:
lifecycle:
preStop:
exec:
command: ["/bin/sh", "-c", "curl --request POST 'localhost:5555/se/grid/node/drain' --header 'X-REGISTRATION-SECRET;'; tail --pid=$(pgrep -f '[n]ode --bind-host false --config /opt/selenium/config.toml') -f /dev/null; sleep 30s"]
command: ["/bin/sh", "-c", "curl --request POST 'localhost:5555/se/grid/node/drain' --header 'X-REGISTRATION-SECRET;'; while curl -fs localhost:5555/status >/dev/null; do sleep 1; done; sleep 10"]
```

That is it, your Selenium Grid pods should now scale up and down properly without any lost sessions!
That is it, your Selenium Grid pods should now scale up and down properly without any lost sessions!