Save S3 Cache

Saves build cache to an arbitrary S3 bucket using a cache key. This Step needs to be used in combination with Restore S3 Cache.

About key-based caching

Key-based caching is a concept where cache archives are saved and restored using a unique cache key. One Bitrise project can have multiple cache archives stored simultaneously, and the Restore S3 Cache Step downloads a cache archive associated with the key provided as a Step input. The Save S3 Cache Step is responsible for uploading the cache archive with an exact key.

Caches can become outdated across builds when something changes in the project (for example, a dependency gets upgraded to a new version). In this case, a new (unique) cache key is needed to save the new cache contents. This is possible if the cache key is dynamic and changes based on the project state (for example, a checksum of the dependency lockfile is part of the cache key). If you use the same dynamic cache key when restoring the cache, the Step will download the most relevant cache archive available.

Key-based caching is platform-agnostic and can be used to cache anything by carefully selecting the cache key and the files/folders to include in the cache.

Templates

The Step requires a string key to use when uploading a cache archive. In order to always download the most relevant cache archive for each build, the cache key input can contain template elements. The Restore S3 cache Step evaluates the key template at runtime and the final key value can change based on the build environment or files in the repo. Similarly, the Save S3 cache Step also uses templates to compute a unique cache key when uploading a cache archive.

The following variables are supported in the Cache key input:

• cache-key-{{ .Branch }}: Current git branch the build runs on
• cache-key-{{ .CommitHash }}: SHA-256 hash of the git commit the build runs on
• cache-key-{{ .Workflow }}: Current Bitrise workflow name (eg. primary)
• {{ .Arch }}-cache-key: Current CPU architecture (amd64 or arm64)
• {{ .OS }}-cache-key: Current operating system (linux or darwin)

Functions available in a template:

checksum: This function takes one or more file paths and computes the SHA256 checksum of the file contents. This is useful for creating unique cache keys based on files that describe content to cache.

Examples of using checksum:

• cache-key-{{ checksum "package-lock.json" }}
• cache-key-{{ checksum "**/Package.resolved" }}
• cache-key-{{ checksum "**/*.gradle*" "gradle.properties" }}

getenv: This function returns the value of an environment variable or an empty string if the variable is not defined.

Examples of getenv:

• cache-key-{{ getenv "PR" }}
• cache-key-{{ getenv "BITRISEIO_PIPELINE_ID" }}

Key matching

The most straightforward use case is when both the Save S3 cache and Restore S3 cache Steps use the same exact key to transfer cache between builds. Stored cache archives are scoped to the Bitrise project. Builds can restore caches saved by any previous Workflow run on any Bitrise Stack.

Unlike this Step, the Restore S3 cache Step can define multiple keys as fallbacks when there is no match for the first cache key. See the docs of the Restore S3 cache Step for more details.

Skip saving the cache

The Step can decide to skip saving a new cache entry to avoid unnecessary work. This happens when there is a previously restored cache in the same workflow and the new cache would have the same contents as the one restored.

Related steps

Restore cache