add support for cgroupv2 by jsvd · Pull Request #18708 · elastic/logstash

jsvd · 2026-02-03T13:56:04Z

With ubuntu 24.04 dropping support for cgroupsv1, it's ideal for Logstash to support cgroupsv2, as other parts of the Stack already do too.

This change introduces cgroupsv2 support and testing for it.

I tested this in a ubuntu 24.04 vm on gcp:

joaoduarte@jsvd-cgroupv2:~$ cat /etc/os-release
PRETTY_NAME="Ubuntu 24.04.4 LTS"
NAME="Ubuntu"
VERSION_ID="24.04"
VERSION="24.04.4 LTS (Noble Numbat)"
VERSION_CODENAME=noble
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=noble
LOGO=ubuntu-logo
joaoduarte@jsvd-cgroupv2:~$ stat -fc %T /sys/fs/cgroup/
cgroup2fs
joaoduarte@jsvd-cgroupv2:~$   ls /sys/fs/cgroup/cpu/ 2>&1
ls: cannot access '/sys/fs/cgroup/cpu/': No such file or directory
joaoduarte@jsvd-cgroupv2:~$   ls /sys/fs/cgroup/memory/ 2>&1
ls: cannot access '/sys/fs/cgroup/memory/': No such file or directory
joaoduarte@jsvd-cgroupv2:~$

And we can see the result of the stack monitoring metrics before the change (no cgroup data):

Logs show error in capturing cgroup data:

joaoduarte@jsvd-cgroupv2:~/logstash-9.3.1$ bin/logstash -e "input { generator {} } output {null{} } " --debug  | grep -e "logstash.instrument.periodicpoller.cgroup"
[2026-03-20T10:30:50,159][DEBUG][logstash.instrument.periodicpoller.cgroup] One or more required cgroup files or directories not found: /proc/self/cgroup, /sys/fs/cgroup/cpuacct, /sys/fs/cgroup/cpu

And with this changeset:

No more error in logs:

joaoduarte@jsvd-cgroupv2:~/logstash$ bin/logstash -e "input { generator {} } output {null{} } " --debug  | grep -e "logstash.instrument.periodicpoller.cgroup"
[2026-03-20T12:30:19,442][DEBUG][logstash.instrument.periodicpoller.cgroup] using cgroupv2

Also still works with v1:

joaoduarte@jsvd-cgroupv1:~/logstash$ bin/logstash -e "input { generator {} } output {null{} } " --debug  | grep -e "logstash.instrument.periodicpoller.cgroup"
Using system java: /usr/bin/java
[2026-03-20T12:35:17,788][DEBUG][logstash.instrument.periodicpoller.cgroup] using cgroupv1

fixes #14534

github-actions · 2026-02-03T13:56:14Z

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Just comment with:

run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)
/run exhaustive tests : Run the exhaustive tests Buildkite pipeline.

mergify · 2026-02-03T13:56:50Z

This pull request does not have a backport label. Could you fix it @jsvd? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
If no backport is necessary, please add the backport-skip label

jsvd · 2026-03-16T19:25:56Z

run exhaustive tests

Separate CGroupV2Resources from CGroupResources for cleaner v1/v2 separation. Try v1 first, fall back to v2 with labeled debug logging.

jsvd · 2026-03-20T10:40:30Z

run exhaustive tests

Detect v1 or v2 on first call and cache the result, avoiding repeated "required cgroup files or directories not found" debug messages.

jsvd · 2026-03-20T12:54:20Z

run exhaustive tests

donoghuc · 2026-03-20T19:33:30Z

logstash-core/lib/logstash/instrument/periodic_poller/cgroup.rb

+
+      private
+
+      def resolve_v2_path


Will this be called often? Should we set an instance variable once then use that for subsequent calls?

donoghuc

Verified by building a container with this branch:
debug log:

[2026-03-20T19:56:53,429][DEBUG][logstash.instrument.periodicpoller.cgroup] using cgroupv2

/_node/stats/os

{
    "os": {
        "cgroup": {
            "cpuacct": {
                "control_group": "/",
                "usage_nanos": 20372769000
            },
            "cpu": {
                "stat": {
                    "number_of_times_throttled": 0,
                    "number_of_elapsed_periods": 0,
                    "time_throttled_nanos": 0
                },
                "control_group": "/",
                "cfs_quota_micros": -1,
                "cfs_period_micros": 100000
            }
        }
    }
}

Left a question/suggestion to "cache" result from a method in an instance var, but its not a blocker. The implementation looks solid 👍

jsvd · 2026-04-01T15:09:42Z

run exhaustive tests

donoghuc · 2026-04-01T16:02:31Z

logstash-core/lib/logstash/instrument/periodic_poller/cgroup.rb

      private

      def resolve_v2_path
+        @v2_path ||= read_v2_path


donoghuc

Looks like we need to manage that state in tests. I tested these suggestions locally and it worked.

donoghuc · 2026-04-01T17:00:21Z

logstash-core/spec/logstash/instrument/periodic_poller/cgroup_spec.rb

+      described_class.instance_variable_set(:@resolved, false)
+      described_class.instance_variable_set(:@active_resources, nil)
+      described_class.instance_variable_set(:@active_label, nil)
+      described_class.instance_variable_set(:@logged_empty, false)


Suggested change

described_class.instance_variable_set(:@logged_empty, false)

described_class.instance_variable_set(:@logged_empty, false)

Cgroup::CGROUP_V2_RESOURCES.instance_variable_set(:@v2_path, nil)

logstash-core/spec/logstash/instrument/periodic_poller/os_spec.rb

elasticmachine · 2026-04-02T09:22:11Z

💛 Build succeeded, but was flaky

Buildkite Build
Commit: 69d9be8

Failed CI Steps

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💔 Build #4565 failed 5914e04
💔 Build #4562 failed d55e26d
💛 Build #4496 was flaky 0e02fd8
💔 Build #4495 failed 13b4a70
💚 Build #4494 succeeded b42d143

jsvd · 2026-04-02T09:57:14Z

run exhaustive tests

jsvd force-pushed the cgroupv2 branch from fc33582 to 9a5ec4c Compare March 16, 2026 18:19

jsvd added 3 commits March 20, 2026 10:38

add support for cgroupv2

ac83029

add integration tests for cgroups v1 and v2

4b060dc

refactor cgroupv2 into separate resource class with better logging

b42d143

Separate CGroupV2Resources from CGroupResources for cleaner v1/v2 separation. Try v1 first, fall back to v2 with labeled debug logging.

jsvd force-pushed the cgroupv2 branch from bdade61 to b42d143 Compare March 20, 2026 10:38

resolve cgroup version once at startup to reduce debug log noise

13b4a70

Detect v1 or v2 on first call and cache the result, avoiding repeated "required cgroup files or directories not found" debug messages.

jsvd marked this pull request as ready for review March 20, 2026 12:55

fix tests

0e02fd8

donoghuc reviewed Mar 20, 2026

View reviewed changes

donoghuc approved these changes Mar 20, 2026

View reviewed changes

memoize read_v2_path

d55e26d

donoghuc approved these changes Apr 1, 2026

View reviewed changes

donoghuc requested changes Apr 1, 2026

View reviewed changes

jsvd added 2 commits April 1, 2026 18:35

test fix

5914e04

test fix

69d9be8

jsvd requested a review from donoghuc April 2, 2026 10:11

	described_class.instance_variable_set(:@logged_empty, false)
	described_class.instance_variable_set(:@logged_empty, false)
	Cgroup::CGROUP_V2_RESOURCES.instance_variable_set(:@v2_path, nil)

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jsvd commented Feb 3, 2026 •

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