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A protobuf schema registry on steroids. It will keep track of the contracts throughout your organization, making sure no contract is broken.
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Protobuf MetaStore


Metastore is a schema registry for Protobuf and gRPC. Metastore main purpose is to be a hub for guarding and distributing your data contracts, be it gRPC service or Protobuf message definitions. It's has a few supported workflows but in general it's meant to be used in conjunction with a git repository and a CI/CD pipeline.

Interaction with the metastore always happens though the API. Updating of the store could happen though CI/CD with metastep, a component meant for running in CI/CD. But the API could also be used in your microservices for usage reporting. But the biggest benefit will come from usage in data pipelines, where they could be build at runtime though getting the contracts over the API.

To have a clear split between configuration (through Options) and contract ownership the metastore has a feature called shadow registry. It makes it possible for other parties, aside the contract owners, too augment the contracts, examples of this could be:

  • Annotate a field to indicate a BigQuery partition column or Cluster column.
  • Add descriptions to fields.
  • Annotate a field to indicate it's a sensitive field (eg. Credit Cart).
  • Annotate a field referencing a message to flatten it into a row.

As metastore does'nt have an API it relies on Git repositories to keep track of contract transactions over time. Metastore is able to commit, pull and push to Git repos where all parties can inspect changes via their favorite Git repository manager.


  • Lint and guard against protobuf/gRPC best practices.
  • Shadow registry, let other users annotate contracts with options, aside from the real contract owners (example data organisation).
  • Multiple storage providers for Memory, Local and Google Cloud Storage. Or write your own.
  • Support multiple registries through one server/API.
  • Finegrained update/verify support though well defined scopes (package prefix, package name, file name, ...)



Metastore presentation at gRPC conf 2019

Known Issues

  • SSH key still need to be configured locally.
  • Metastep needs to be retested and only focused on GitLab now.


  • Implement the resource (example Pub/Sub or Kafka topic) to contract mapping (Message descriptor).
  • Better Git commit messages.
  • Donate the registry API to the gRPC project.
  • Act as a global gRPC reflection Server.

Quick setup

This quick setup is needed when you want to build Metastore by yourself, begin by creating the file gradle/properties.gradle

ext {
    snapshotRepoUrl = "https ://you.maven.repo.example/repository/maven-snapshots/"
    repoUrl = "https ://you.maven.repo.example/repository/maven-releases/"
    repoUser = "repo_user"
    repoPass = "supersecret"

    containerRepoBase = ""
    containerRepoTarget = ""

Build the base images that jib uses, see in base directory.

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