Example Provider

This is an example of a Node provider that uses Pact, Pactflow and Travis CI to ensure that it is compatible with the expectations its consumers have of it.

The project uses a Makefile to simulate a very simple build pipeline with two stages - test and deploy.

It is using a public tenant on Pactflow, which you can access here using the credentials dXfltyFMgNOFZAxr8io9wJ37iUpY42M/O5AIZWxelWbLvqMd8PkAVycBJh2Psyg1. The latest version of the Example Consumer/Example Provider pact is published here.

Pact verifications

When using Pact in a CI/CD pipeline, there are two reasons for a pact verification task to take place:

• When the provider changes (to make sure it does not break any existing consumer expectations)
• When a pact changes (to see if the provider is compatible with the new expectations)

When the provider changes, the pact verification task runs as part the provider's normal build pipeline, generally after the unit tests, and before any deployment takes place. This pact verification task is configured to dynamically fetch all the relevant pacts for the specified provider from Pactflow, verify them, and publish the results back to Pactflow.

To ensure that a verification is also run whenever a pact changes, we create a webhook in Pactflow that triggers a provider build, and passes in the URL of the changed pact. Ideally, this would be a completely separate build from your normal provider pipeline, and it should just verify the changed pact.

Because Travis CI only allows us to have one build configuration per repository, we switch between the main pipeline mode and the webhook-triggered mode based on the presence of an environment variable that is only set via the webhook. Keep in mind that this is just a constraint of the tools we're using for this example, and is not necessarily the way you would implement Pact your own pipeline.

Features

• In .travis.yml

  • Our PACT_BROKER_TOKEN environment variable is encrypted. This is a read/write token. For normal development use, you would use a read only token, as you would not be publishing verification results from your local machine.
  • In the script section, we switch between running the target for the normal provider build pipeline, and the webhook-triggered pact verification target, based on whether or not the $PACT_URL is set. The $PACT_URL will be set when this build has been trigged by a 'contract content changed' webhook (more on this later). This switch is just required because Travis only lets us have one build configuration file per repository - usually you would define a completely separate job in your CI for the pact changed webhook.

• In the Makefile:

  • The target create_or_update_travis_webhook creates the Pactflow webhook that will trigger a build of the provider when any of its consumers publishes a pact with changed content.
  • To call the Travis API that triggers the build, the webhook uses a bearer token that is stored in a Pactflow secret called ${user.travisToken}. The secret can be created using the create_travis_token_secret target, or through the Pactflow UI.
  • The target ci runs when the provider has pushed a new commit. It performs the following tasks:
    • Run the isolated tests (including the pact verification tests, which publish the verification results)
    • If we are on master:
      • Check if we are safe to deploy to prod using can-i-deploy (ie. do we have a succesfully verified pact with the version of the consumer that is currently in production)
      • Deploy (just pretend!)
      • Tag the deployed application version as prod in Pactflow so Pactflow knows which version of the provider is in production when the consumer runs can-i-deploy.
  • The target ci_webhook just runs the pact verification step, and is used when the build is triggered by the webhook.

• In src/product/product.pact.test.js:

  • When the $PACT_URL is not set (ie. the build is running because the provider changed), the provider is configured to fetch all the pacts for the 'example-provider' provider which belong to the latest consumer versions tagged with master and prod. This ensures the provider is compatible with the latest changes that the consumer has made, and is also backwards compatible with the production version of the consumer.
  • When the $PACT_URL is set (ie. the build is running because it was triggered by the 'contract content changed' webhook), we just verify the pact at the $PACT_URL.
  • Pact-JS has a very flexible verification task configuration that allows us to use the same code for both the main pipeline verifications and the webhook-triggered verifications, with dynamically set options. Depending on your pact implementation, you may need to define separate tasks for each of these concerns.
  • When the verification results are published, the provider version number is set to the git sha, and the provider version tag is the git branch name. You can read more about versioning here.

Usage

See the Pactflow CI/CD Workshop.