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[docker-in-docker] Use iptables-legacy only if it's working #1425

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[docker-in-docker] Use iptables-legacy only if it's working #1425

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8fc69f4
[docker-in-docker] Use iptables-legacy only if it's working
olivierlemasle Jul 30, 2025
77b8ec0
Add test, bump version
olivierlemasle Aug 6, 2025
ee2ed47
Fix unload kernel module ip_tables
olivierlemasle Aug 8, 2025
7b59ca9
Test with module ip_tables
olivierlemasle Aug 8, 2025
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2 changes: 1 addition & 1 deletion src/docker-in-docker/install.sh
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Hello @olivierlemasle ,

Would you kindly add test for this fix. Also please do a version bump.

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@olivierlemasle olivierlemasle Aug 6, 2025 •
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Hello @Kaniska244,

Do you have any suggestion on how to test this fix? The error depends on if the ip_tables kernel module is loaded on the host, so a test needs to access the host kernel 🤔.

Actually, when the host kernel does not have the ip_tables module loaded, the generated tests already fail, and this is fixed with this PR.

E.g. on Fedora 42 system (host), with kernel module ip_tables not loaded (this can be reproduced with modprobe -r ip_tables), the command

devcontainer features test -f docker-in-docker --skip-scenarios --skip-duplicated -i debian:12

fails with:

🏃 Starting test(s)...

🧪 Starting 'docker-in-docker' tests...


🔄 Testing 'version'

Docker version 28.3.3-1, build 980b85681696fbd95927fd8ded8f6d91bdca95b0


✅  Passed 'version'!


🔄 Testing 'docker-init-exists'

/usr/local/share/docker-init.sh


✅  Passed 'docker-init-exists'!


🔄 Testing 'docker-ps'

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?


❌ docker-ps check failed.
🧹 Cleaning up 1 test containers...
🧹 Removing container 03e19c445011...



  ================== TEST REPORT ==================
❌ Failed:      'docker-in-docker'

This is fixed with the PR:

🏃 Starting test(s)...

🧪 Starting 'docker-in-docker' tests...


🔄 Testing 'version'

Docker version 28.3.3-1, build 980b85681696fbd95927fd8ded8f6d91bdca95b0


✅  Passed 'version'!


🔄 Testing 'docker-init-exists'

/usr/local/share/docker-init.sh


✅  Passed 'docker-init-exists'!


🔄 Testing 'docker-ps'

CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES


✅  Passed 'docker-ps'!


🔄 Testing 'log-exists'

/tmp/dockerd.log


✅  Passed 'log-exists'!


🔄 Testing 'log-for-completion'

time="2025-08-06T12:58:32.864310897Z" level=info msg="Daemon has completed initialization"


✅  Passed 'log-for-completion'!


🔄 Testing 'log-contents'

time="2025-08-06T12:58:32.864568877Z" level=info msg="API listen on /var/run/docker.sock"


✅  Passed 'log-contents'!


🔄 Testing 'moby-buildx'

moby-buildx     0.26.0-debian12u1


✅  Passed 'moby-buildx'!


Test Passed!
🧹 Cleaning up 1 test containers...
🧹 Removing container 767628a63e7d...



  ================== TEST REPORT ==================
✅ Passed:      'docker-in-docker'

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@Kaniska244 Kaniska244 Aug 6, 2025 •
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Hello @olivierlemasle ,

Indeed that's a very pertinent question. How do we get a fedora host/ VM to test this? Let me check on this and also discuss with the maintainers and get back to you.

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A Fedora host is not required, but at least an environment where it is possible to manage kernel modules.

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@olivierlemasle olivierlemasle Aug 6, 2025 •
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I've actually found a way to add a test. It is actually possible to load/unload kernel modules on Github Actions environment. However, unloading the module currently works on CI environment only when I run my added scenario, not when all scenarios are run. Still working on it.

Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,7 @@ if ! type git > /dev/null 2>&1; then
fi

# Swap to legacy iptables for compatibility
if type iptables-legacy > /dev/null 2>&1; then
if type iptables-legacy > /dev/null 2>&1 && iptables-legacy -L > /dev/null 2>&1; then
update-alternatives --set iptables /usr/sbin/iptables-legacy
update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy
fi
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