Bazel GitOps Rules

Bazel GitOps Rules provides tooling to bridge the gap between Bazel (for hermetic, reproducible, container builds) and continuous, git-operation driven, deployments. Users author standard kubernetes manifests and kustomize overlays for their services. Bazel GitOps Rules handles image push and substitution, applies necessary kustomizations, and handles content addressed substitutions of all object references (configmaps, secrets, etc). Bazel targets are exposed for applying the rendered manifest directly to a Kubernetes cluster, or into version control facilitating deployment via Git operations.

Bazel GitOps Rules is an alternative to rules_k8s. The main differences are:

• Utilizes and integrates the full set of Kustomize capabilities for generating manifests.
• Implements GitOps target.
• Supports personal namespace deployments.
• Provides integration test setup utility.
• Speeds up deployments iterations:
  • The results manifests are rendered without pushing containers.
  • Pushes all the images in parallel.
• Provides an utility that creates GitOps pull requests.

Rules

• k8s_deploy
• k8s_test_setup

Guides

• Base Manifests and Overlays
• Generating Configmaps
• Injecting Docker Images
• Adding Dependencies
• GitOps and Deployment
• Integration Testing Support

Installation

From the release you wish to use: https://github.com/adobe/rules_gitops/releases copy the WORKSPACE snippet into your WORKSPACE file.

k8s_deploy

The k8s_deploy creates rules that produce the .apply and .gitops targets k8s_deploy is defined in k8s.bzl. k8s_deploy takes the files listed in the manifests, patches, and configmaps_srcs attributes and combines (renders) them into one YAML file. This happens when you bazel build or bazel run a target created by the k8s_deploy. The file is created at bazel-bin/path/to/package/name.yaml. When you run a .apply target, it runs kubectl apply on this file. When you run a .gitops target, it copies this file to the appropriate location in the same os separate repository.

For example, let's look at the example's k8s_deploy. We can peek at the file containing the rendered K8s manifests:

cd examples
bazel run //helloworld:mynamespace.show

When you run bazel run ///helloworld:mynamespace.apply, it applies this file into your personal ({BUILD_USER}) namespace. Viewing the rendered files with .show can be useful for debugging issues with invalid or misconfigured manifests.

Base Manifests and Overlays

The manifests listed in the manifests attribute are the base manifests used by the deployment. This is where the important manifests like Deployments, Services, etc. are listed.

The base manifests will be modified by most of the other k8s_deploy attributes like substitutions and images. Additionally, they can be modified to configure them different clusters/namespaces/etc. using overlays.

To demonstrate, let's go over hypothetical multi cluster deployment.

Here is the fragment of the k8s_deploy rule that is responsible for generating manifest variants per CLOUD, CLUSTER, and NAMESPACE :

k8s_deploy(
    ...
    manifests = glob([                 # (1)
      "manifests/*.yaml",
      "manifests/%s/*.yaml" % (CLOUD),
    ]),
    patches = glob([                   # (2)
      "overlays/*.yaml",
      "overlays/%s/*.yaml" % (CLOUD),
      "overlays/%s/%s/*.yaml" % (CLOUD, NAMESPACE),
      "overlays/%s/%s/%s/*.yaml" % (CLOUD, NAMESPACE, CLUSTER),
    ]),
    ...
)

The manifests list (1) combines common base manifests and CLOUD specific manifests.

manifests
├── aws
│   └── pvc.yaml
├── onprem
│   ├── pv.yaml
│   └── pvc.yaml
├── deployment.yaml
├── ingress.yaml
└── service.yaml

Here we see that aws and onprem clouds have different persistence configurations aws/pvc.yaml and onprem/pvc.yaml.

The patches list (2) requires more granular configuration that introduces 3 levels of customization: CLOUD, NAMESPACE, and CLUSTER. Each manifest fragment in the overlays subtree applied as strategic merge patch update operation.

overlays
├── aws
│   ├── deployment.yaml
│   ├── prod
│   │   ├── deployment.yaml
│   │   └── us-east-1
│   │       └── deployment.yaml
│   └── uat
│       └── deployment.yaml
└── onprem
    ├── prod
    │   ├── deployment.yaml
    │   └── us-east
    │       └── deployment.yaml
    └── uat
        └── deployment.yaml

That looks like a lot. But lets try to decode what is happening here:

1. aws/deployment.yaml adds persistent volume reference specific to all AWS deployments.
2. aws/prod/deployment.yaml modifies main container CPU and memory requirements in production configurations.
3. aws/prod/us-east-1/deployment.yaml adds monitoring sidecar.

Generating Configmaps

Configmaps are a special case of manifests. They can be rendered from a collection of files of any kind (.yaml, .properties, .xml, .sh, whatever). Let's use hypothetical Grafana deployment as an example:

[
    k8s_deploy(
        name = NAME,
        cluster = CLUSTER,
        configmaps_srcs = glob([                 # (1)
            "configmaps/%s/**/*" % CLUSTER
        ]),
        configmaps_renaming = 'hash',            # (2)

        ...
    )
    for NAME, CLUSTER, NAMESPACE in [
        ("mynamespace", "dev", "{BUILD_USER}"),  # (3)
        ("prod-grafana", "prod", "prod"),        # (4)
    ]
]

Here we generate two k8s_deploy targets, one for mynamespace (3), another for production deployment (4).

The directory structure of configmaps looks like this:

grafana
└── configmaps
    ├── dev
    │   └── grafana
    │       └── ldap.toml
    └── prod
        └── grafana
            └── ldap.toml

The configmaps_srcs parameter (1) will get resolved into the patterns configmaps/dev/**/* and configmaps/prod/**/*. The result of rendering the manifests bazel run //grafana:prod-grafana.show will have following manifest fragment:

apiVersion: v1
data:
  ldap.toml: |
    [[servers]]
    ...
kind: ConfigMap
metadata:
  name: grafana-k75h878g4f
  namespace: ops-prod

The name of directory on the first level of glob patten grafana become the configmap name. The ldap.toml file on the next level were embedded into the configmap.

In this example, the configmap renaming policy (2) is set to hash, so the configmap's name appears as grafana-k75h878g4f. (If the renaming policy was None, the configmap's name would remain as grafana.) All the references to the grafana configmap in other manifests are replaced with the generated name:

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
      volumes:
      ...
      - configMap:
          items:
          - key: ldap.toml
            path: ldap.toml
          name: grafana-k75h878g4f
        name: grafana-ldap

Injecting Docker Images

Third-party Docker images can be referenced directly in K8s manifests, but for most apps, we need to run our own images. The images are built in the Bazel build pipeline using rules_docker. For example, the java_image rule creates an image of a Java application from Java source code, dependencies, and configuration.

Here's a (very contrived) example of how this ties in with k8s_deploy. Here's the BUILD file located in the package //examples:

java_image(
    name = "helloworld_image",
    srcs = glob(["*.java"]),
    ...
)
k8s_deploy(
    name = "helloworld",
    manifests = ["helloworld.yaml"],
    images = {
        "helloworld_image": ":helloworld_image",  # (1)
    }
)

And here's helloworld.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: helloworld
spec:
  containers:
    - image: //examples:helloworld_image  # (2)

There images attribute dictionary (1) defines the images available for the substitution. The manifest file references the fully qualified image target path //examples:helloworld_image (2).

The image key value in the dictionary is used as an image push identifier. The best practice (as provided in the example) is to use image key that matches the label name of the image target.

When we bazel build the example, the rendered manifest will look something like this:

apiVersion: v1
kind: Pod
metadata:
  name: helloworld
spec:
  containers:
    - image: registry.example.com/examples/helloworld_image@sha256:c94d75d68f4c1b436f545729bbce82774fda07

The image substitution using an images key is supported, but not recommended (this functionality might be removed in the future). For example, helloworld.yaml can reference helloworld_image:

apiVersion: v1
kind: Pod
metadata:
  name: helloworld
spec:
  containers:
    - image: helloworld_image

Image substitutions for Custom Resource Definitions (CRD) resources could also use target references directly. Their digests are available through string substitution. For example,

apiVersion: v1
kind: MyCrd
metadata:
  name: my_crd
  labels:
    app_label_image_digest: "{{//examples:helloworld_image.digest}}"
    app_label_image_short_digest: "{{//examples:helloworld_image.short-digest}}"
spec:
  image: "{{//examples:helloworld_image}}"

would become

apiVersion: v1
kind: MyCrd
metadata:
  name: my_crd
  labels:
    app_label_image_digest: "e6d465223da74519ba3e2b38179d1268b71a72f"
    app_label_image_short_digest: "e6d465223d"
spec:
  image: registry.example.com/examples/helloworld_image@sha256:e6d465223da74519ba3e2b38179d1268b71a72f

An all examples above the image: URL points to the helloworld_image in the private Docker registry. The image is uploaded to the registry before any .apply or .gitops target is executed. See helloworld for a complete example.

As with the rest of the dependency graph, Bazel understands the dependencies k8s_deploy has on the Docker image and the files in the image. So for example, here's what will happen if someone makes a change to one of the Java files in helloworld_image and then runs bazel run //examples:helloworld.apply:

1. The helloworld_image will be rebuilt with the new code and uploaded to the registry
2. A new helloworld manifest will be rendered using the new image
3. The new helloworld pod will be deployed

It is possible to use alternative ways to resolve images as long as respective rule implements K8sPushInfo provider. For example, this setup will mirror the referred image into a local registry and provide a reference to it. k8s_deploy will need to use image_pushes parameter:

load("@com_fasterci_rules_mirror//mirror:defs.bzl", "mirror_image")
mirror_image(
    name = "agnhost_image",
    digest = "sha256:93c166faf53dba3c9c4227e2663ec1247e2a9a193d7b59eddd15244a3e331c3e",
    dst_prefix = "gcr.io/myregistry/mirror",
    src_image = "registry.k8s.io/e2e-test-images/agnhost:2.39",
)
k8s_deploy(
    name = "agnhost",
    manifests = ["agnhost.yaml"],
    image_pushes = [
        ":agnhost_image",
    ]
)

Adding Dependencies

Many instances of k8s_deploy include an objects attribute that references other instances of k8s_deploy. When chained this way, running the .apply will also apply any dependencies as well.

For example, to add dependency to the example helloworld deployment:

k8s_deploy(
    name = "mynamespace",
    objects = [
        "//other:mynamespace",
    ],
    ...
)

When you run bazel run //helloworld:mynamespace.apply, it'll deploy a helloword and other service instance into your namespace.

Please note that the objects attribute is ignored by .gitops targets.

GitOps and Deployment

The simplified CI pipeline that incorporates GitOps will look like this:

[Checkout Code] -> [Bazel Build & Test] -> (if GitOps source branch) -> [Create GitOps PRs]

The Create GitOps PRs step usually is the last step of a CI pipeline. rules_gitops provides the create_gitops_prs command line tool that automates the process of creating pull requests.

For the full list of create_gitops_prs command line options, run:

bazel run @com_adobe_rules_gitops//gitops/prer:create_gitops_prs

Supported Git Servers

The --git_server parameter defines the type of a Git server API to use. The supported Git server types are github, gitlab, and bitbucket.

Depending on the Git server type the create_gitops_prs tool will use following command line parameters:

Trunk Based GitOps Workflow

For example let's assume the CI build pipeline described above is running the build for https://github.com/example/repo.git. We are using trunk based branching model. All feature branches are merged into the master branch first. The Create GitOps PRs step runs on a master branch change. The GitOps deployments source files are located in the same repository under the /cloud directory.

The Create GitOps PRs pipeline step shell command will look like following:

GIT_ROOT_DIR=$(git rev-parse --show-toplevel)
GIT_COMMIT_ID=$(git rev-parse HEAD)
GIT_BRANCH_NAME=$(git rev-parse --abbrev-ref HEAD)
if [ "${GIT_BRANCH_NAME}" == "master"]; then
    bazel run @com_adobe_rules_gitops//gitops/prer:create_gitops_prs -- \
        --workspace $GIT_ROOT_DIR \
        --git_repo https://github.com/example/repo.git \
        --git_mirror $GIT_ROOT_DIR/.git \
        --git_server github \
        --release_branch master \
        --gitops_pr_into master \
        --gitops_pr_title "This is my pull request title" \
        --gitops_pr_body "This is my pull request body message" \
        --branch_name ${GIT_BRANCH_NAME} \
        --git_commit ${GIT_COMMIT_ID} \
fi

The GIT_* variables describe the current state of the Git repository.

The --git_repo parameter defines the remote repository URL. In this case remote repository matches the repository of the working copy. The --git_mirror parameter is an optimization used to speed up the target repository clone process using reference repository (see git clone --reference). The --git-server parameter selects the type of Git server.

The --release_branch specifies the value of the release_branch_prefix attribute of gitops targets (see k8s_deploy). The --gitops_pr_into defines the target branch for newly created pull requests. The --branch_name and --git_commit are the values used in the pull request commit message.

The create_gitops_prs tool will query all gitops targets which have set the deploy_branch attribute (see k8s_deploy) and the release_branch_prefix attribute value that matches the release_branch parameter.

The all discovered gitops targets are grouped by the value of deploy_branch attribute. The one deployment branch will accumulate the output of all corresponding gitops targets.

For example, we define two deployments: grafana and prometheus. Both deployments share the same namespace. The deployments a grouped by namespace.

[
    k8s_deploy(
        name = NAME,
        deploy_branch = NAMESPACE,
        ...
    )
    for NAME, CLUSTER, NAMESPACE in [
        ...
        ("stage-grafana", "stage", "monitoring-stage"),
        ("prod-grafana", "prod", "monitoring-prod"),
    ]
]
[
    k8s_deploy(
        name = NAME,
        deploy_branch = NAMESPACE,
        ...
    )
    for NAME, CLUSTER, NAMESPACE in [
        ...
        ("stage-prometheus", "stage", "monitoring-stage"),
        ("prod-prometheus", "prod", "monitoring-prod"),
    ]
]

As a result of the setup above the create_gitops_prs tool will open up to 2 potential deployment pull requests:

• from deploy/monitoring-stage to master including manifests for stage-grafana and stage-prometheus
• from deploy/monitoring-prod to master including manifests for prod-grafana and prod-prometheus

The GitOps pull request is only created (or new commits added) if the gitops target changes the state for the target deployment branch. The source pull request will remain open (and keep accumulation GitOps results) until the pull request is merged and source branch is deleted.

The --stamp parameter allows for the replacement of certain placeholders, but only when the gitops target changes the output's digest compared to the one already saved. The new digest of the unstamped data is also saved with the manifest. The digest is kept in a file in the same location as the YAML file, with a .digest extension added to its name. This is helpful when the manifests have volatile information that shouldn't be the only factor causing changes in the target deployment branch.

Here are the placeholders that can be replaced:

--dry_run parameter can be used to test the tool without creating any pull requests. The tool will print the list of the potential pull requests. It is recommended to run the tool in the dry run mode as a part of the CI test suite to verify that the tool is configured correctly.

Multiple Release Branches GitOps Workflow

In the situation when the trunk based branching model in not suitable the create_gitops_prs tool supports creating GitOps pull requests before the code is merged to master branch.

Both trunk and release branch workflow could coexists in the same repository.

For example, let's assume the CI build pipeline described above is running the build for https://github.com/example/repo.git. We are using release branch branching model. Feature request are merged into multiple target release branches. The release brach name convention is release/team-<YYYYMMDD>. The Create GitOps PRs step is running on the release branch change. GitOps deployments source files are located in the same repository /cloud directory in the master branch.

The Create GitOps PRs pipeline step shell command will look like following:

GIT_ROOT_DIR=$(git rev-parse --show-toplevel)
GIT_COMMIT_ID=$(git rev-parse HEAD)
GIT_BRANCH_NAME=$(git rev-parse --abbrev-ref HEAD)          # => release/team-20200101
RELEASE_BRANCH_SUFFIX=${GIT_BRANCH_NAME#"release/team"}     # => -20200101
RELEASE_BRANCH=${GIT_BRANCH_NAME%${RELEASE_BRANCH_SUFFIX}}  # => release/team
if [ "${RELEASE_BRANCH}" == "release/team"]; then
    bazel run @com_adobe_rules_gitops//gitops/prer:create_gitops_prs -- \
        --workspace $GIT_ROOT_DIR \
        --git_repo https://github.com/example/repo.git \
        --git_mirror $GIT_ROOT_DIR/.git \
        --git_server github \
        --release_branch ${RELEASE_BRANCH} \
        --deployment_branch_suffix=${RELEASE_BRANCH_SUFFIX} \
        --gitops_pr_into master \
        --gitops_pr_title "This is my pull request title" \
        --gitops_pr_body "This is my pull request body message" \
        --branch_name ${GIT_BRANCH_NAME} \
        --git_commit ${GIT_COMMIT_ID} \
fi

The meaning of the parameters is the same as with trunk based workflow. The --release_branch parameter takes the value of release/team. The additional parameter --deployment_branch_suffix will add the release branch suffix to the target deployment branch name.

If we modify previous example:

[
    k8s_deploy(
        name = NAME,
        deploy_branch = NAMESPACE,
        release_branch_prefix = "release/team",  # will be selected only when --release_branch=release/team
        ...
    )
    for NAME, CLUSTER, NAMESPACE in [
        ...
        ("stage-grafana", "stage", "monitoring-stage"),
        ("prod-grafana", "prod", "monitoring-prod"),
    ]
]
[
    k8s_deploy(
        name = NAME,
        deploy_branch = NAMESPACE,
        release_branch_prefix = "release/team",  # will be selected only when --release_branch=release/team
        ...
    )
    for NAME, CLUSTER, NAMESPACE in [
        ...
        ("stage-prometheus", "stage", "monitoring-stage"),
        ("prod-prometheus", "prod", "monitoring-prod"),
    ]
]

The result of the setup above the create_gitops_prs tool will open up to 2 potential deployment pull requests per release branch. Assuming release branch name is release/team-20200101:

• from deploy/monitoring-stage-20200101 to master including manifests for stage-grafana and stage-prometheus
• from deploy/monitoring-prod-20200101 to master including manifests for prod-grafana and prod-prometheus

Integration Testing Support

Note: the Integration testing support has known limitations and should be considered experimental. The public API is subject to change.

Integration tests are defined in BUILD files like this:

k8s_test_setup(
    name = "service_it.setup",
    kubeconfig = "@k8s_test//:kubeconfig",
    objects = [
        "//service:mynamespace",
    ],
)

java_test(
    name = "service_it",
    srcs = [
        "ServiceIT.java",
    ],
    data = [
        ":service_it.setup",
    ],
    jvm_flags = [
        "-Dk8s.setup=$(location :service_it.setup)",
    ],
    # other attributes omitted for brevity
)

The test is composed of two rules, a k8s_test_setup rule to manage the Kubernetes setup and a java_test rule that executes the actual test.

The k8s_test_setup rule produces a shell script which creates a temporary namespace (the namespace name is your username followed by five random digits) and creates a kubeconfig file that allows access to this new namespace. Inside the namespace, it creates some objects specified in the objects attributes. In the example, there is one target here: //service:mynamespace. This target represents a file containing all the Kubernetes object manifests required to run the service.

The output of the k8s_test_setup rule (a shell script) is referenced in the java_test rule. It's listed under the data attribute, which declares the target as a dependency, and is included in the jvm flags in this clause: $(location :service_it.setup). The "location" function is specific to Bazel: given a target, it returns the path to the file produced by that target. In this case, it returns the path to the shell script created by our k8s_test_setup rule.

The test code launches the script to perform the test setup. The test code should also monitor the script console output to listen to the pod readiness events.

The @k8s_test//:kubeconfig target referenced from k8s_test_setup rule serves the purpose of making Kubernetes configuration available in the test sandbox. The kubeconfig repository rule in the WORKSPACE file will need, at minimum, provide the cluster name.

load("@com_adobe_rules_gitops//gitops:defs.bzl", "kubeconfig")

kubeconfig(
    name = "k8s_test",
    cluster = "dev",
)

k8s_test_setup

Note: the k8s_test_setup rule is an experimental feature and is subject to change.

An executable that performs Kubernetes test setup:

• creates temporary namespace
• creates kubectl configuration with the default context set to the created namespace
• deploys all dependent objects
• forwards service ports

kubeconfig

Note: the kubeconfig repository rule is an experimental feature and is subject to change.

Configures Kubernetes tools for testing.

Building & Testing

Building & Testing GitOps Rules

bazel test //...

Building & Testing Examples Project

cd examples
bazel test //...

Have a Question

Find the rules_gitops contributors in the #gitops channel on the Bazel Slack.

Contributing

Contributions are welcomed! Read the Contributing Guide for more information.

Adopters

Here's a (non-exhaustive) list of companies that use rules_gitops in production. Don't see yours? You can add it in a PR!

• Adobe (Advertising Cloud)
• FasterCI
• Skydio

Licensing

The contents of third party dependencies in /vendor folder are covered by their repositories' respective licenses.

The contents of /templating/fasttemplate are licensed under MIT License. See LICENSE for more information.

All other files are licensed under the Apache V2 License. See LICENSE for more information.