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@willcl-ark willcl-ark commented Jul 16, 2025

This changeset migrates all current self-hosted CI jobs over to hosted Cirrus Runners.

These runners cost a flat rate of $150/month, and we qualify for an open source discount of 50%. Therefore they are $75/month/runner.

One "runner" should more accurately be thought of in terms of the number of vCPU you are purchasing: https://cirrus-runners.app/pricing/ or in terms of "concurrency", where 1 runners gets you 1.0 concurrency.
e.g. a Linux x86 Runner gets you 16 vCPU (1.0 concurrency) and 64GB RAM to be provisioned as you choose, amongst one or more jobs.

Cirrus Runners currently only support Linux (x86 and Arm64) and MacOS (Arm64).
This changeset does not move the existing Github Actions native MacOS runners away from being run on Github's infrastructure. This could be a follow up optimisation.

Runs from this changeset using Cirrus Runners can be found at: https://github.com/testing-cirrus-runners/bitcoin2/actions which shows an uncached run on master (CI#1), an outside pull request (CI#3) and an updated push to master (CI#4).

These workflows were run on 10 runners, and we would recommend purchasing a similar number for our CI in this repo to achieve the speed and concurrency we expect.

We include some optional performance commits, but these could be split out and made into followups or dropped entirely.

Benefits

Maintenance

As we are not self-hosting, nobody needs to maintain servers, disks etc.

Bus factor

Currently we have a very small number of people with the know-how working on server setup and maintenance. This setup fixes that so that "anyone" familiar with GitHub-style CI systems can work on it.

Scaling

These do not "auto-scale"/have "unlimited concurrency" like some solutions, but if we want more workers/cpu to increase parallism or increase the runner size of certain jobs for a speed-up we can simply buy more concurrency using the web interface.

Speed

Runtimes aproximate current runtimes pretty well, with some jobs being faster.
Caching improvements on pull request (re-runs) are left as future optimisations from the current changeset (see below).

GitHub workflow syntax

With a migration to the more-commonly-used GitHub workflow syntax, migration to other providers in the future is often as simple as a one-line change (and installing a new GitHub app to the repo).

If we decide to self-host again, then we can also self-host GitHub runners (using https://github.com/actions/runner) and maintain new GH-style CI syntax.

Reporting

GitHub workflows provide nicer built-in reporting directly on the "Checks" page of a pr. This includes more-detailed action reporting, and a host of pretty nice integrated features, such as Workflow Commands for creating annotations that can print messages during runs. See for example at the bottom of this window where we report ccache hitrate, if it was below 90%: https://github.com/testing-cirrus-runners/bitcoin/actions/runs/16163449125?pr=1

These could be added conditionally into our CI scripts to report interesting or other information.

Costs

Financial

Relative to competitors Cirrus runners are cheap for the hosted CI-world. However these are likely more expensive than our current setup, or a well-configured (new) self-hosted setup.

If we started with 10 runners to be shared amongst all migrated jobs, this would total $750/mo = $9000/yr.

Note that we are not trying to comptete here on cost directly.

Dependencies

We would be dependent on Cirrus infra.

Forks

  • Forks should be able to run CI without paid Cirrus runners. This behaviour is achieved through a rather verbose runs-on: directive.
    • This directive hardcodes the main repo (unfortunately you cannot use the env github context in this field in particular, for some reason).
    • This directive also allows for a fork to patch the runs-on: field in the ci.yml file if they want to use Cirrus Runners too.
    • The workflow otherwise will fallback to the GitHub free runners on forks.
  • This cirrus cache action transparently falls back to github actions cache when not running on cirrus, so forks will get some free github caching (10GB per repo).

All jobs work on forks, but will run (slowly) on GitHub native free hosted runners, instead of Cirrus runners. They will also suffer from poor cache hit-rates, but there's nothing that can be done about that, and the situtation is an improvement on today.

Migration process

The main org should also, in addition to pulling code changes:

  1. Permit the actions docker/setup-buildx-action@v3 and docker/login-action@v3 to be run in this repo.

Caching

For the number of CI jobs we have, cache usage on GitHub would be an issue as GH only provides 10GB of cache space, per repo. However cirrus provides 10 GB per runner, which scales better with the number of runners.

The cirruslabs/action/[restore|save] action we use here redirects this to Cirrus' own cache and is both faster and larger.

In the case that user is running CI on a fork, the cirrus cache falls back transparently to GitHub default cache without error.

ccache, depends-sources, built-depends

  • Cached as blobs via cirruslabs/actions/cache action.
  • Current implementation:
    • On push: restores and saves caches.
    • On pull_request: restores but does not save caches.

This means a new pull request should hit a pretty relevant cache.
Old pull requests which are not being rebased on master may suffer from lower cache hit-rate.

If we save caches on all pull request runs we run the risk of evicting recent (and more relevant) cache blobs.
It may be possible in a future optimisation to widen this to save on pull request runs too, but it will also depend on how many runners we provision and what cache churn rates are like in the main repo.

Docker build layer caching

  • Cached using the gha cache backend
  • These cache blobs compete for space with ccache, depends-sources and depends-built caches
  • gha cache allows --cache-from to be used from pull requests, which does not work using a registry cache type (technically we could use a public read-only token to get this working, but that feels wrong)

This backend does network i/o and so are marginally slower than our current disk i/o cache.

But what about... x?

We have tested many other providers, including Runs-on, Buildjet, WarpBuild, and GitHub hosted runners (and investigated even more). But they all fall short in one-way or another.

  • Runs-On and Buildjet (and others) require installing GH apps with much too-liberal permissions (e.g. Administration: Read|Write) for our use-case.
  • GitHub hosted runners suffer from all of high costs, lower speed, small cache, and the requirement for a GitHub Teams subscription.
  • WarpBuild seems to be simply too expensive.

TODO:

To complete migration from self-hosted to hosted for this repo, the backport branches 27.x, 28.x and 29.x would also need their CI ported, but these are left for followups to this change (and pending review/changes here first).


Work and experimentation undertaken with m3dwards

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DrahtBot commented Jul 16, 2025

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32989.

Reviews

See the guideline for information on the review process.

Type Reviewers
ACK janb84, maflcko, m3dwards, achow101
Concept ACK fanquake, hebasto, 0xB10C, stickies-v

If your review is incorrectly listed, please react with 👎 to this comment and the bot will ignore it on the next update.

Conflicts

Reviewers, this pull request conflicts with the following ones:

  • #33145 (CI: silent merge check by m3dwards)
  • #33051 (Don't fix Python patch version by Sjors)
  • #31425 (RFC: Riscv bare metal CI job by TheCharlatan)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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Concept ACK. This will also need to go back to 27.x.

@willcl-ark
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willcl-ark commented Jul 16, 2025

Concept ACK. This will also need to go back to 27.x.

Testing a backport to 29.x here: https://github.com/testing-cirrus-runners/bitcoin2/actions/runs/16320536543

I think the best course of action could be to look for a little more conceptual review here, and after that squash the "ci: port x" commits in this changeset down to a single one, to make backporting to the multiple supported branches easier.

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Concept ACK

@maflcko
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maflcko commented Jul 17, 2025

This means a new pull request should hit a pretty relevant cache.
Old pull requests which are not being rebased on master may suffer from lower cache hit-rate.

I don't think this is true. A pull request that modifies a core header (like serialize.h) will now always start from a cold cache. The current persistent workers have a high ccache hit rate for pulls that are (force) pushed for minor fixups (https://0xb10c.github.io/bitcoin-core-ci-stats/graph/ccache/). Also, before CI runs, pull requests are rebased/merged with master, so the age of a pull request alone shouldn't affect cache hit rate.

However, the trade-offs here are probably worth to go forward and try to optimize the ccache hit rate later. Concept ACK.

Give the robot account read/write access to this repo

This seems a bit scary. Are you saying that a proprietary third party outside of our control can now push directly to the repo? My assumption was that the tokens would be added to CI in this repo and CI had write access to the registry, not the other way round. Why would the registry need write access here?

Edit: We may reconsider #31850 and drop container image caching, and just accept the intermittent network IO errors or network speed issues.

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This means a new pull request should hit a pretty relevant cache.
Old pull requests which are not being rebased on master may suffer from lower cache hit-rate.

I don't think this is true. A pull request that modifies a core header (like serialize.h) will now always start from a cold cache. The current persistent workers have a high ccache hit rate for pulls that are (force) pushed for minor fixups (0xb10c.github.io/bitcoin-core-ci-stats/graph/ccache). Also, before CI runs, pull requests are rebased/merged with master, so the age of a pull request alone shouldn't affect cache hit rate.

However, the trade-offs here are probably worth to go forward and try to optimize the ccache hit rate later. Concept ACK.

Yes, force pushes for minor fixups is the tradeoff we have in the current implementation. As you say, we can set the ccache to save on pull requests too (in the future) if necessary.

Give the robot account read/write access to this repo

This seems a bit scary. Are you saying that a proprietary third party outside of our control can now push directly to the repo? My assumption was that the tokens would be added to CI in this repo and CI had write access to the registry, not the other way round. Why would the registry need write access here?

Sorry for not being clearer! The robot account gets read/write access to the Quay.io (docker) repo, not this code repository!

Edit: We may reconsider #31850 and drop container image caching, and just accept the intermittent network IO errors or network speed issues.

Yes, I would love to get #31850 working in any case, as it would simply avoid long rebuilds in the worst cases; most docker images are rebuilding in < 2 minutes, except MSAN...

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I guess you want review here and then address it, as it comes in? Once review is finished, the app will be installed and reviewers can also look at a "real" run in this repo?

looked at c0ad2b6~23 🎬

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Concept ACK.

we qualify for an open source discount of 50%.

We would be dependent on Cirrus infra...

We shouldn't be surprised when Cirrus suddenly changes its modus operandi, including its advertised open-source discount or general availability.

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Concept ACK.

we qualify for an open source discount of 50%.

We would be dependent on Cirrus infra...

We shouldn't be surprised when Cirrus suddenly changes its modus operandi, including its advertised open-source discount or general availability.

Certainly, it is good to be wary of that. I think this is equally true for all cloud providers though.

It's my belief that if we complete this migration we are resonably well protected against this risk for the following reasons:

  1. As we use the common GitHub workflow yaml format, changing to another provider can be as simple as amending the runs-on: line in the yaml (and installing a different provider's GH app, and changing the cache action to that provider's own).
  2. We could always revert back to a self-hosted solution utilizing the new workflow yaml via https://github.com/actions/runner, which for example can be trivially configured on one or more self-hosted servers using services.github.runner with Nix (I have a demo of such a configuration here).

We seem to have a good working relationship so far with Cirrus, @m3dwards has a responsive and helpful contact there. Of course, we are in the tendering stage so there is perhaps extra impetus to be helpful to us, but I don't see any reason that a historical precedence of limiting free runners (which are allegedly being abused for crypto mining), should appear any more risky to paid/premium customers (than any other provider).

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maflcko commented Jul 17, 2025

2. We could always revert back to a self-hosted solution

Agree that this may happen with any third party (including GitHub itself). If we want to switch back to the self-hosted runners, it should be as trivial as git revert $the_merge_commit_of_this_pull. Alternatively, switch to GHA-based self-hosted runners. Though, it would be good to create a proof-of-concept pull request to switch to self-hosted runners in GHA, or a different hosted alternative (e.g. warp-build), after this pull is merged. This makes it easier to see that (1) it works and (2) how easily it is possible.

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Pushed c126475 with a CI run on master branch at https://github.com/testing-cirrus-runners/bitcoin2/actions/runs/16368410249

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willcl-ark commented Jul 18, 2025

Thanks for the review @maflcko & @fanquake , I hope I addressed all your current review comments.

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0xB10C commented Jul 18, 2025

Concept ACK!

I think finishing the migration would close #31965

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looked at c126475~20 💇

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Thanks for the review on this so far.

Whilst we had tested the docker registry caching on PRs successfully, because I was opening them myself (and was owner of the parent repo) repo-level variables were available to me which were not available to 3rd party pull requests.

The short of this is that this meant the docker registry cache setup could not pull from the registry on pull requests and we didn't think it was therefore suitable for our purposes.

We have switched to the gha cache backend in the latest force-push with the good news that we finally have it working for all images correctly; caching to/from on pushes, and caching from on pulls.

A push to master can be found here: https://github.com/testing-cirrus-runners/bitcoin2/actions/runs/16529929752

And a pull request (from a 3rd party account) here: https://github.com/testing-cirrus-runners/bitcoin2/actions/runs/16531270443?pr=3

A new commit has been added, 0bd758e, to fix a (new?) issue we experienced with the asan job where the runner host appeared to update it's image and kernel. The cached docker image for the ASAN job then had the incorrect linux-headers-<version> package installed, causing the job to fail. There are likely multiple ways to fix this (we could input uname as a docker build arg for example), but simply forcing a reinstall of the correct headers in 03_*.sh seemed easiest. Open to suggestions here however...

Marking as ready for review now, as I think this is conceptually ready.

@willcl-ark willcl-ark marked this pull request as ready for review July 25, 2025 21:45
willcl-ark and others added 16 commits September 1, 2025 16:22
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>
Removed as unused.
Previously jobs were running on a large multi-core server where 10 jobs
as default made sense (or may even have been on the low side).

Using hosted runners with fixed (and lower) numbers of vCPUs we should
adapt compilation to match the number of cpus we have dynamically.

This is cross-platform compatible with macos and linux only.
Print the ccache hit-rate for the job using a GitHub annotation if it
was below 75%.
Docker currently warns that we are missing a default value.

Set this to scratch which will error if an appropriate image tag is not
passed in to silence the warning.
ci/lint_run.sh: Only used in .cirrus.yml. Refer to test/lint/README.md on how to run locally.
ci/lint_run_all.sh: Only used in .cirrus.yml for stale re-runs of old pull request tasks.
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re ACK 3c5da69

changes since last ACK:

  • changed cirrus-runner for 32 bit ARM

@DrahtBot DrahtBot requested a review from maflcko September 1, 2025 16:38
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maflcko commented Sep 2, 2025

re-ACK 3c5da69 🏗

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m3dwards commented Sep 2, 2025

ACK 3c5da69

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achow101 commented Sep 2, 2025

ACK 3c5da69

Not particularly familiar with github actions or the cirrus, but it seems like all of the tasks that we were running on cirrus previously are correctly ported over and working.

@fanquake fanquake merged commit ba0b430 into bitcoin:master Sep 3, 2025
39 of 40 checks passed
@@ -26,6 +26,7 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
--file "${BASE_READ_ONLY_DIR}/ci/test_imagefile" \
--build-arg "CI_IMAGE_NAME_TAG=${CI_IMAGE_NAME_TAG}" \
--build-arg "FILE_ENV=${FILE_ENV}" \
--build-arg "BASE_ROOT_DIR=${BASE_ROOT_DIR}" \
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nit in 9c2b96e: Actually, on a second thought, this seems a bit fragile. It seems this would break the use-case of using several different local folders to run the CI, because the CI images have different, non-deterministic, paths embedded?

I presume the correct fix would be to download the sdk to a hard-coded path in the container image, and then adjust the pre-existing rsync call to copy it at runtime in the container, if needed.

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maflcko commented Sep 3, 2025

To complete migration from self-hosted to hosted for this repo, the backport branches 27.x, 28.x and 29.x would also need their CI ported, but these are left for followups to this change (and pending review/changes here first).

27.x looks close to EOL in one month, according to https://bitcoincore.org/en/lifecycle/, so I guess it could just die with the old CI?

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fanquake commented Sep 3, 2025

Yea. I think it's fine to leave 27.x as is, this just needs backporting to 29.x & 28.x.

@@ -284,7 +301,8 @@ jobs:
windows-cross:
name: 'Linux->Windows cross, no tests'
runs-on: ubuntu-latest
needs: runners
runs-on: ${{ needs.runners.outputs.use-cirrus-runners == 'true' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md' || 'ubuntu-24.04' }}
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nit: Any reason to use md here? Most of the time 7/8 CPUs will be idle (to download the caches or to upload the artifact). Also, the similar mac-cross build is using sm.

Suggested diff:

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6876b8328d..2efe17a04e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -302,7 +302,7 @@ jobs:
   windows-cross:
     name: 'Linux->Windows cross, no tests'
     needs: runners
-    runs-on: ${{ needs.runners.outputs.use-cirrus-runners == 'true' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md' || 'ubuntu-24.04' }}
+    runs-on: ${{ needs.runners.outputs.use-cirrus-runners == 'true' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-sm' || 'ubuntu-24.04' }}
     if: ${{ vars.SKIP_BRANCH_PUSH != 'true' || github.event_name == 'pull_request' }}
 
     env:
@@ -433,7 +433,7 @@ jobs:
             file-env: './ci/test/00_setup_env_arm.sh'
 
           - name: 'ASan + LSan + UBSan + integer, no depends, USDT'
-            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-lg' # has to match container in ci/test/00_setup_env_native_asan.sh for tracing tools
+            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md' # has to match container in ci/test/00_setup_env_native_asan.sh for tracing tools
             fallback-runner: 'ubuntu-24.04'
             timeout-minutes: 120
             file-env: './ci/test/00_setup_env_native_asan.sh'
@@ -445,7 +445,7 @@ jobs:
             file-env: './ci/test/00_setup_env_mac_cross.sh'
 
           - name: 'No wallet, libbitcoinkernel'
-            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md'
+            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-sm'
             fallback-runner: 'ubuntu-24.04'
             timeout-minutes: 120
             file-env: './ci/test/00_setup_env_native_nowallet_libbitcoinkernel.sh'
@@ -481,7 +481,7 @@ jobs:
             file-env: './ci/test/00_setup_env_native_tidy.sh'
 
           - name: 'TSan, depends, no gui'
-            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-lg'
+            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md'
             fallback-runner: 'ubuntu-24.04'
             timeout-minutes: 120
             file-env: './ci/test/00_setup_env_native_tsan.sh'
@@ -528,7 +528,7 @@ jobs:
   lint:
     name: 'lint'
     needs: runners
-    runs-on: ${{ needs.runners.outputs.use-cirrus-runners == 'true' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-sm' || 'ubuntu-24.04' }}
+    runs-on: ${{ needs.runners.outputs.use-cirrus-runners == 'true' && 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-xs' || 'ubuntu-24.04' }}
     if: ${{ vars.SKIP_BRANCH_PUSH != 'true' || github.event_name == 'pull_request' }}
     timeout-minutes: 20
     env:

This will also reduce the machine for the asan task, which similarly spends 20 (!) minutes in a single test on a single CPU (tool_signet_miner). (Using a larger runner won't help here speed this test up). I'd say maybe the test should be adjusted to be faster.

Also, the linters are single-threaded, so are good with the smallest instance.

And tsan and nowallet seem to be fine with a smaller instance as well.

The patch overall should free up 1.5 instances to be used in pull requests in parallel. Thoughts?

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Runner size wasn't extensively tested for performance, your logic for going for smaller runners seems sound to me.

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