New Bazel Ruleset Helps Developers Build Secure Container Images

Google has made it simpler and more secure to build container images using the Bazel build system.

Bazel, an open source build and test tool similar to Make and Maven, supports projects in multiple languages and builds for multiple platforms. Developers use Starlark, a human-readable, high-level build language, to create rules instructing Bazel on what to do. A rule specifies the input files and the type of output that would be generated as a result, such as an executable or a library file. Related rules are combined into a ruleset, such as rules for creating binaries and running tests.

Bazel can be used to create Distroless builds, or minimal base images where what is in the runtime container is restricted to only components necessary for the application. Minimal base images reduce the burden of managing risks associated with security vulnerabilities in the components and address governance issues in the software supple chain.

The new rules_oci ruleset “modernizes” the process for creating Distroless builds by adding supply chain security metadata to the container images, Google Open Source Security Team’s Appu Goundan wrote in the post announcing the general availability of rules_oci. Because Bazel supports managing and caching dependencies by their integrity hash, it can make assurances about the supply chain. Developers get a software bill of materials showing what went into the container, allowing organizations to make informed decisions about the images they are using.

Code signing allows users to verify that the container image was not modified by someone else after it was created by the developer who signed it.

The new rules_oci ruleset allows developers using Bazel to create Docker containers instead of using the older rules_docker ruleset, which is now in maintenance mode. The advantage new ruleset has over the older one is that it allows developers to create Docker containers even if a docker daemon is not already installed on the machine. There is a Migration guide to help organizations move from using rules_docker to rules_oci.