Remote build

Remote build is a feature in Snapcraft that offloads the build process to Launchpad’s build farm and enables developers to build snaps for different architectures.

Architectures supported by Launchpad can be found here.

Open vs closed source

By default, prospective snaps must be open source because the build will be publicly available.

Developers are reminded of this by confirming that their project will be publicly available when starting a remote build. This prompt can be automatically agreed to by passing --launchpad-accept-public-upload.

Closed-source projects can be built using the remote builder. This requires the user to create a private Launchpad project and pass the project with the --project <project-name> command line argument. An ssh key must be registered in Launchpad because source code is uploaded using SSH.

Git repository

Projects must be in the top level of a git repository because snapcraft uses a git-based workflow to upload projects to Launchpad.

Shallowly cloned repositories are not supported (e.g. git clone --depth 1) because git does not support pushing shallow clones.

Versions

Two versions of the remote-builder are available, the current and the legacy remote-builder.

Current

The current remote builder is available for core22, core24, and newer snaps. It is not available for core20 snaps because it cannot parse core20’s snapcraft.yaml schema ([10]).

It does not modify the project or project metadata.

Legacy

The “fallback” or legacy version of the remote builder can be used for core20 and core22 snaps. It is not available for core24 and newer snaps.

The legacy remote builder was deprecated because of its design. It retrieves and tarballs remote sources and modifies the project’s snapcraft.yaml file to point to the local tarballs. This caused many unexpected failures that could not be reproduced locally.

Choosing a remote-builder

The environment variable SNAPCRAFT_REMOTE_BUILD_STRATEGY determines which remote-builder is used:

  • disable-fallback will use the current remote builder

  • force-fallback will use the legacy remote builder

If the environment variable is unset, the remote builder will be determined by the base:

  • core22, core24, and newer snaps will use the current remote builder

  • core20 snaps will use the legacy remote builder

Platforms and architectures

Remote builds can be orchestrated for multiple platforms and architectures.

Current

--platform and --build-for

Note

--platform and --build-for behave differently than they do for lifecycle commands.

--platform or --build-for can only be provided when the platforms or architectures keywords are not defined in the project metadata ([12]).

These keywords are mutually exclusive and must be a comma-separated list of debian architectures.

core22 snaps can only use --build-for. core24 and newer snaps can use --platform or --build-for.

Project platforms and architectures

The snapcraft.yaml file is always parsed by the new remote builder.

If the project metadata contains a platforms or architectures entry, Snapcraft will request a build for each unique build-for architecture.

Note

Launchpad does not support cross-compiling ([13]).

Note

Launchpad does not support building multiple snaps on the same build-on architecture ([14]).

If the project metadata does not contain a platforms or architectures entry and no --build-for or --platform are passed, Snapcraft will request a build on, and for, the host’s architecture.

The remote builder does not work for core20 snaps because it cannot parse the run-on keyword in a core20 architecture entry ([2]).

Legacy

--build-for and --build-on

The Launchpad build farm was designed for native builds and does not have a concept of a build-for architecture.

The legacy remote builder accepts --build-on and --build-for. Since developers are typically interested in the build-for of a snap, snapcraft converts the --build-for to --build-on.

These parameters are not mutually exclusive and --build-for takes precedence over --build-on.

Both of these parameters accept a comma-separated list of architectures. Snapcraft will request builds to occur on each specified architecture.

Project architectures

If the snapcraft.yaml file contains the top-level architectures keyword, snapcraft will request a build for each build-on architecture.

An architecture can only be listed once across all build-on keys in the architectures keyword, otherwise Snapcraft will fail to parse the project ([4]).

If no architectures are defined in the project metadata, snapcraft will request a build for the host’s architecture.

--build-for and --build-on cannot be provided when the architectures keyword is defined in the project metadata. This is because Launchpad will ignore the requested architectures and prefer those defined in the snapcraft.yaml ([5]).

The legacy remote builder can be used for core20 and core22 snaps but the project is parsed using core20’s snapcraft.yaml schema. This means that snaps using keywords introduced in core22 cannot be built with the remote builder ([6] [7] [8]). This includes the core22 architectures keyword change of run-on to build-for.

Similarly, core22 supports a shorthand notation for architectures but Launchpad is not able to parse this notation ([9]).