How Calyptia fixed its Arm builds whilst saving money

Learn how Calyptia fixed its failing Arm builds for open-source Fluent Bit and accelerated our commercial development by adopting Actuated and bare-metal runners.

This is a case-study, and guest article by Patrick Stephens, Tech Lead of Infrastructure at Calyptia.


Different architecture builds can be slow using the Github Actions hosted runners due to emulation of the non-native architecture for the build. This blog shows a simple way to make use of self-hosted runners for dedicated builds but in a secure and easy to maintain fashion.

Calyptia maintains the OSS and Cloud Native Computing Foundation (CNCF) graduated Fluent projects including Fluent Bit. We then add value to the open-source core by providing commercial services and enterprise-level features.

Fluent Bit is a Fast and Lightweight Telemetry Agent for Logs, Metrics, and Traces for Linux, macOS, Windows, and BSD family operating systems. It has been made with a strong focus on performance to allow the collection and processing of telemetry data from different sources without complexity.

It was originally created by Eduardo Silva and is now an independent project.

To learn about Fluent Bit, the Open Source telemetry agent that Calyptia maintains, check out their docs.

The Problem

One of the best things about Fluent Bit is that we provide native packages (RPMs and DEBs) for a myriad of supported targets (various Linux, macOS and Windows), however to do this is also one of the hardest things to support due to the complexity of building and testing across all these targets.

When PRs are provided we would like to ensure they function across the targets but doing so can take a very long time (hours) and consume a lot of resources (that must be paid for). This means that these long running jobs are only done via exception (manually labelling a PR or on full builds for releases) leading to issues only discovered when a full build & test is done, e.g. during the release process so blocking the release until it is fixed.

The long build time problem came to a head when we discovered we could no longer build for Amazon Linux 2023 (AL2023) because the build time exceeded the 6 hour limit for a single job on Github. We had to disable the AL2023 target for releases which means users cannot then update to the latest release leading to missing features or security problems: See the issue here

In addition to challenges in the OSS, there are also challenges on the commercial side. Here, we are seeing issues with extended build times for ARM64 targets because our CI is based on Github Actions and currently only AMD64 (also called x86-64 or x64) runners are provided for builds. This slows down development and can mean bugs are not caught as early as possible.

Why not use self-hosted runners?

One way to speed up builds is to provide self-hosted ARM64 runners.

Unfortunately, runners pose security implications, particularly for public repositories. In fact, Github recommends against using self-hosted runners: About self-hosted runners - GitHub Docs

In addition to security concerns, there are also infrastructure implications for using self-hosted runners. We have to provide the infrastructure around deploying and managing the self-hosted runners, installing an agent, configuring it for jobs, etc. From a perspective of OSS we want anything we do to be simple and easy for maintenance purposes.

Any change we make needs to be compatible with downstream forks as well. We do not want to break builds for existing users, particularly for those who are contributors as well to the open source project. Therefore we need a solution that does not impact them.

There are various tools that can help with managing self-hosted runners, provides a good curated list. I performed an evaluation of some of the recommended tools but the solution would be non-trivial and require some effort to maintain.

Our considerations

We have the following high level goals in a rough priority order:

  • Speed up the build.
  • Keep costs minimal.
  • Keep the process as secure as possible.
  • Make it simple to deploy and manage.
  • Minimise impact to OSS forks and users.

The solution

At Kubecon EU 2023 I met up with Alex Ellis from Actuated (and of OpenFaaS fame) in-person and we wanted to put Alex and his technology to the test, to see if the Actuated technology could fix the problems we see with our build process.

To understand what Actuated is then it is best to refer to their documentation with this specific blog post being a good overview of why we considered adopting it. We're not the only CNCF project that Alex's team was able to help. He describes how he helped Parca and Network Service Mesh to slash their build teams by using native Arm hardware.

A quick TLDR; though would be that Actuated provides an agent you install which then automatically creates ephemeral VMs on the host for each build job. Actuated seemed to tick the various boxes (see the considerations above) we had for it but never trust a vendor until you’ve tried it yourself!

Quote from Alex:

"Actuated aims to give teams the closest possible experience to managed runners, but with native arm support flat rate billing, and secure VM-level isolation. Since Calyptia adopted actuated, we’ve also shipped an SSH debug experience (like you’d find with CircleCI) and detailed reports and insights on usage across repos, users and organisations."

To use Actuated, you have to provision a machine with the Actuated agent, which is trivial and well documented:

We deployed an Ampere Altra Q80 server with 256GB of RAM and 80 cores ARM64 machine via Equinix (Equinix donates resources to the CNCF which we use for Fluent Bit so this satisfies the cost side of things) and installed the Actuated agent on it per the Actuated docs.

The update required to start using Actuated in OSS Fluent Bit is a one-liner. (Thanks in part to my excellent work refactoring the CI workflows, or so I like to think. You can see the actual PR here for the change:

The following is the code required to start using Actuated:

-    runs-on: ubuntu-latest
+    runs-on: ${{ (contains(matrix.distro, 'arm' ) & 'actuated-arm64') || 'ubuntu-latest' }}

For most people, the change will be much simpler:

-    runs-on: ubuntu-latest
+    runs-on: actuated

In Github Actions parlance, the code above translates to “if we are doing an ARM build, then use the Actuated runner; otherwise, use the default Github Hosted (AMD64) Ubuntu runner”.

In the real code, I added an extra check so that we only use Actuated runners for the official source repo which means any forks will also carry on running as before on the Github Hosted runner.

With this very simple change, all the ARM64 builds that used to take hours to complete now finish in minutes. In addition, we can actually build the AL2023 ARM64 target to satisfy those users too. A simple change gave us a massive boost to performance and also provided a missing target.

To demonstrate this is not specific to Equinix hosts or in some fashion difficult to manage in heterogeneous infrastructure (e.g. various hosts/VMs from different providers), we also replicated this for all our commercial offerings using a bare-metal Hetzner host. The process was identical: install the agent and make the runs-on code change as above to use Actuated. Massive improvements in build time were seen again as expected.

The usage of bare-metal (or cloud) hosts providers is invisible and only a choice of which provider you want to put the agent on. In our case we have a mixed set up with no difference in usage or maintenance.

Challenges building containers

The native package (RPM/DEB) building described above was quite simple to integrate via the existing workflows we had.

Building the native packages is done via a process that runs a target-specific container for each of the builds, e.g. we run a CentOS container to build for that target. This allows a complete build to be run on any Linux-compatible machine with a container runtime either in CI or locally. For ARM builds, we were using QEMU emulation for ARM builds hence the slowdown as this has to emulate instructions between architectures.

Container builds are the primary commercial area for improvement as we provide a SAAS solution running on K8S. Container builds were also a trickier proposition for OSS as we were using a single job to build all architectures using the docker/build-push-action. The builds were incredibly slow for ARM and also atomic, which means if you received a transient issue in one of the architecture builds, you would have to repeat the whole lot.

As an example:

      - name: Build the production images
        id: build_push
        uses: docker/build-push-action@v4
          file: ./dockerfiles/Dockerfile
          context: .
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          platforms: linux/amd64, linux/arm64, linux/arm/v7
          target: production
          # Must be disabled to provide legacy format images from the registry
          provenance: false
          push: true
          load: false
          build-args: |
            FLB_NIGHTLY_BUILD=${{ inputs.unstable }}
            RELEASE_VERSION=${{ inputs.version }}

The build step above is a bit more complex to tease out into separate components: we need to run single architecture builds for each target then provide a multi-arch manifest that links them together.

We reached out to Alex on a good way to modify this to work within a split build per architecture approach. The Actuated team has been very responsive on these types of questions along with proactive monitoring of our build queue and runners.

Within Calyptia we have followed the approach Docker provided here and suggested by the Actuated team:

Based on what we learned, we recommend the following process is followed:

Build each architecture and push by digest in a set of parallel matrix jobs. Capture the output digest of each build. Create the multi-arch manifest made up of each digest we have pushed in step 1 using the artefact from step 2.

This approach provides two key benefits. First, it allows us to run on dedicated runners per-arch. Second, if a job fails we only need to repeat the single job, instead of having to rebuild all architectures.

The new approach reduced the time for the release process for the Calyptia Core K8S Operator from more than an hour to minutes. Additionally, because we can do this so quickly, we now build all architectures for every change rather than just on release. This helps developers who are running ARM locally for development as they have containers always available.

The example time speed up for the Calyptia Core K8S operator process was replicated across all the other components. A very good bang for your buck!

For us, the actuated subscription fee has been of great value. Initially we tested the waters on the Basic Plan, but soon upgraded when we saw more areas where we could use it. The cost for us has been offset against a massive improvement in CI time and development time plus reducing the infrastructure costs of managing the self-hosted runners.

Lessons learned

The package updates were seamless really, however we did encounter some issues with the ecosystem (not with actuated), when refactoring and updating our container builds. The issues with the container builds are covered below to help anyone else with the same problems.

Provenance is now enabled by default

We were using v3 of Docker’s docker/build-push-action, but they made a breaking change which caused us a headache. They changed the default in v4 to create the various extra artifacts for provenance (e.g. SBOMs) which did have a few extra side effects both at the time and even now.

If you do not disable this then it will push manifest lists rather than images so you will subsequently get an error message when you try to create a manifest list of another manifest list.

Separately this also causes issues for older docker clients or organisations that need the legacy Docker schema format from a registry: using it means only OCI format schemas are pushed. This impacted both OSS and our commercial offerings:

It meant people on older OS’s or with requirements on only consuming Docker schema (e.g. maybe an internal mirror registry only supports that) could not pull the images.

Invalid timestamps for with manifests

A funny problem found with our cloud-run deployments for Calyptia Core SAAS offering was that pushing the manifests to (Google Container Registry) meant they ended up with a zero-epoch timestamp. This messed up some internal automation for us when we tried to get the latest version.

To resolve this we just switched back to doing a single architecture build as we do not need multi-arch manifests for cloud-run. Internally we still have multi-arch images in for internal use anyway, this is purely the promotion to

Manifests cannot use sub-paths

This was a fun one: when specifying images to make up your manifest they must be in the same registry of course!

Now, we tend to use sub-paths a lot to handle specific use cases for but unfortunately you cannot use them when trying to construct a manifest.

OK: --> NOK: -->

As with all good failures, the tooling let me make a broken manifest at build time but unfortunately trying to pull it meant a failure at runtime.

Actuated container registry mirror

All Github hosted runners provide default credentials to authenticate with for pulling public images. When running on a self-hosted runner you need to authenticate for this otherwise you will hit rate limits and builds may fail as they cannot download required base images.

Actuated provide a registry mirror and Github Action to simplify this so make sure you set it up:

As part of this, ensure it is set up for anything that uses images (e.g. we run integration tests on KIND that failed as the cluster could not download its images) and that it is done after any buildx config as it creates a dedicated buildx builder for the mirror usage.

Actuated support

The Actuated team helped us in two ways: the first was that we were able to enable Arm builds for our OSS projects and our commercial products, when they timed out with hosted runners. The second way was where our costs were getting out of hand on GitHub’s larger hosted runners: Actuated not only reduced the build time, but the billing model is flat-rate, meaning our costs are now fixed, rather than growing.

As we made suggestions or collaborated with the Actuated team, they updated the documentation, including our suggestions on smoothing out the onboarding of new build servers and new features for the CLI.

The more improvements we’ve made, the more we’ve seen. Next on our list is getting the runtime of a Go release down from 26 minutes by bringing it over to actuated.


Alex Ellis: We've learned a lot working with Patrick and Calyptia and are pleased to see that they were able to save money, whilst getting much quicker, and safer Open Source and commercial builds.

We value getting feedback and suggestions from customers, and Patrick continues to provide plenty of them.

If you'd like to learn more about actuated, reach out to speak to our team by clicking "Sign-up" and filling out the form. We'll be in touch to arrange a call.