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kube-applier

Forked from: https://github.com/box/kube-applier

kube-applier is Kubernetes deployment tool strongly following gitOps principals. It enables continuous deployment of Kubernetes objects by applying declarative configuration files from a Git repository to a Kubernetes cluster.

kube-applier runs as a Deployment in your cluster and watches the Git repo to ensure that the cluster objects are up-to-date with their associated spec files (JSON or YAML) in the repo.

Configuration is done through the kube-applier.io/Waybill CRD. Each namespace in a cluster defines a Waybill CRD which defines the source of truth for the namespace inside the repository.

Whenever a new commit to the repo occurs, or at a specified interval, kube-applier performs a "run", issuing kubectl apply commands at namespace level.

kube-applier serves a status page and provides metrics for monitoring.

Usage

Please refer to the command line -help for information on the various configuration options. Each flag corresponds to an environment variable (eg.: -repo-path is REPO_PATH).

They are all optional values expect for -repo-remote which is required for kube-applier to start.

Waybill CRD

kube-applier behaviour is controlled through the Waybill CRD. Refer to the code or CRD yaml definition for details, an example with the default values is shown below:

apiVersion: kube-applier.io/v1alpha1
kind: Waybill
metadata:
  name: main
spec:
  autoApply: true
  delegateServiceAccountSecretRef: kube-applier-delegate
  dryRun: false
  gitSSHSecretRef:
    name: ""
    namespace: ""
  prune: true
  pruneClusterResources: false
  pruneBlacklist: []
  repositoryPath: <namespace-name>
  runInterval: 3600
  runTimeout: 900
  serverSideApply: false
  strongboxKeyringSecretRef:
    name: ""
    namespace: ""

See the documentation on the Waybill CRD spec for more details.

Delegate ServiceAccount

To avoid leaking access from kube-applier to client namespaces, the concept of a delegate ServiceAccount is introduced. When applying a Waybill, kube-applier will use the credentials defined in the Secret referenced by delegateServiceAccountSecretRef. This is a ServiceAccount in the same namespace as the Waybill itself and should typically be given admin access to the namespace. See the client base for an example of how to set this up.

This secret should be version controlled but will have to be manually applied at first in order to bootstrap the kube-applier integration in a namespace.

Integration with strongbox

strongbox is an encryption tool, geared towards Git repositories and working as a Git filter.

If strongboxKeyringSecretRef is defined in the Waybill spec (it is an object that contains the attributes name and namespace), it should reference a Secret resource which contains a key named .strongbox_keyring or .strongbox_identity with the value being a valid Strongbox keyring or identity file. That keyring/identity is subsequently used when applying the Waybill, allowing for decryption of files under the repositoryPath. If the attribute namespace for strongboxKeyringSecretRef is not specified then it defaults to the same namespace as the Waybill itself.

This secret should be readable by the ServiceAccount of kube-applier. If deployed using the provided kustomize bases, kube-applier's ServiceAccount will have read access to secrets named "kube-applier-strongbox-keyring" by default. Alternatively, if you need to use a different name, you will need to create a Role and a RoleBinding to give "get" permission to it.

If you need to deploy a shared strongbox keyring to use in multiple namespaces, the Secret should have an annotation called "kube-applier.io/allowed-namespaces" which contains a comma-seperated list of all the namespaces that are allowed to use it.

For example, the following secret can be used by namespaces "ns-a", "ns-b" and "ns-c", assuming its deployed in ns-a:

# ./kustomization.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

secretGenerator:
  - name: kube-applier-strongbox-keyring
    files:
      - .strongbox_keyring=strongbox-keyring
      - .strongbox_identity=strongbox-identity
    options:
      annotations:
        kube-applier.io/allowed-namespaces: "ns-b, ns-c"

# ./strongbox-keyring

keyentries:
- description: mykey
  key-id: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
  key: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

# ./strongbox-identity

# description: ident1
# public key: age1ex4ph3ryaathfac0xpjhxk50utn50mtprke7h0vsmdlh6j63q5dsafxehs
AGE-SECRET-KEY-1GNC98E3WNPAXE49FATT434CFC2THV5Q0SLW45T3VNYUVZ4F8TY6SREQR9Q

Each item in the list of allowed namespaces supports shell pattern matching, meaning you can grant access to namespaces based on naming conventions:

kube-applier.io/allowed-namespaces: "team-a-*, team-b-monitoring"

The secret containing the strongbox keyring should itself be version controlled to prevent kube-applier from pruning it. However, since it is a secret itself and would need be encrypted as well in git, it must be created manually the first time (or after any changes to its contents).

Private Kustomize Bases

If not overridden via Waybill.Spec.gitSSHSecretRef configuration (see below), Kube-Applier will use the SSH key passed via -git-ssh-key-path as the default key flag to try fetching remote kustomize bases from private repositories. Since this relies on using SSH to fetch from upstreams, the bases should be defined with the ssh:// scheme in kustomization.yaml.

Custom SSH Keys

You can specify custom SSH keys to be used for fetching remote kustomize bases from private repositories. In order to do that, you will need to specify gitSSHSecretRef: it should reference a Secret that contains one or more SSH keys that provide access to the private repositories that contain these bases.

In this Secret, items with a name that begins with "key_*" are treated as SSH keys to be used with kustomize. Additionally this Secret can optionally define a value for "known_hosts". If ommitted, git will use ssh with StrictHostKeyChecking disabled.

To use an SSH key for Kustomize bases, the bases should be defined with the ssh:// scheme in kustomization.yaml and have a # kube-applier: key_foobar comment above it. For example:

bases:
  # https scheme (default if omitted), any SSH keys defined are ignored
  - github.com/utilitywarehouse/kube-applier//testdata/bases/simple-deployment?ref=master
  # ssh scheme requires a valid SSH key to be defined
  # kube-applier: key_a
  - ssh://github.com/utilitywarehouse/kube-applier//testdata/bases/simple-deployment?ref=master

This Secret can be shared in the same way that a strongbox keyring can be shared, as shown in the example below:

kind: Secret
apiVersion: v1
metadata:
  name: kube-applier-git-ssh
  namespace: ns-a
  annotations:
    kube-applier.io/allowed-namespaces: "ns-b, ns-c"
stringData:
  key_a: |-
    -----BEGIN OPENSSH PRIVATE KEY-----
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==
    -----END OPENSSH PRIVATE KEY-----
  key_b: |-
    -----BEGIN OPENSSH PRIVATE KEY-----
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==
    -----END OPENSSH PRIVATE KEY-----
  known_hosts: |-
    github.com ssh-rsa AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==

Resource pruning

Resource pruning is enabled by default and controlled by the prune attribute of the Waybill spec. This means that if a file is removed from the git repository, the resources defined in it will be pruned in the next run.

If you want kube applier to prune cluster resources, you can set pruneClusterResources to true. Take care when using this feature as it will remove all cluster resources that have been created by kubectl and don't exist in the current namespace directory. Therefore, only use this feature if all of your cluster resources are defined under one directory.

Specific resource types can be exempted from pruning by adding them to the pruneBlacklist attribute:

  pruneBlacklist:
    - core/v1/ConfigMap
    - core/v1/Namespace

To blacklist resources for all namespaces, use the PRUNE_BLACKLIST environment variable:

env:
  - name: PRUNE_BLACKLIST
    value: "core/v1/ConfigMap,core/v1/Namespace"

The resource apps/v1/ControllerRevision is always exempted from pruning, regardless of the blacklist. This is because Kubernetes copies the kubectl.kubernetes.io/last-applied-configuration annotation to controller revisions from the corresponding StatefulSet, Deployment or Daemonset. This would result in kube-applier pruning revisions that it shouldn't be managing if it wasn't blacklisted.

It's important to note that kube-applier uses a SelfSubjectRulesReview to establish which resources it has permissions to prune. This may not work reliably if you aren't using the RBAC authorization module. In which case, the prune allowlist may be empty or incomplete.

Deploying

Included is a Kustomize (https://kustomize.io/) base you can reference in your namespace:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
bases:
- github.com/utilitywarehouse/kube-applier//manifests/base/server?ref=<version>

and patch as per example: manifests/example/

Note that the example also includes the client base, for kube-applier to manage its own namespace.

Please note that if you enable kustomize for your namespace and you've enabled pruning in kube-applier, all your resources need to be listed in your kustomization.yaml under resources. If you don't do this kube-applier will assume they have been removed and start pruning.

Additionally, you will need to deploy the following kustomize base that includes cluster-level resources (also see this section if you are using the pruneClusterResources attribute):

github.com/utilitywarehouse/kube-applier//manifests/base/cluster?ref=<version>

Monitoring

Status UI

kube-applier serves an HTML status page on which displays information about the Waybills managed by it and their most recent apply runs, including:

  • Apply run type (reason)
  • Start times and latency
  • Most recent commit
  • Apply command, output and errors

The HTML template for the status page lives in templates/status.html, and static/ holds additional assets.

Metrics

kube-applier uses Prometheus for metrics. Metrics are hosted on the webserver at /__/metrics. In addition to the Prometheus default metrics, the following custom metrics are included:

  • kube_applier_run_latency_seconds - A Histogram that keeps track of the durations of each apply run, labelled with the namespace name, a success and a dry run boolean.

  • kube_applier_namespace_apply_count - A Counter for each namespace that has had an apply attempt over the lifetime of the container, incremented with each apply attempt and labelled by the namespace and the result of the attempt.

  • kube_applier_result_summary - A Gauge for each resource, labelled with the namespace, action, status and type of object applied.

  • kube_applier_kubectl_exit_code_count - A Counter for each exit code returned by executions of kubectl, labelled with the namespace and exit code.

  • kube_applier_last_run_timestamp_seconds - A Gauge that reports the last time a run finished, expressed in seconds since the Unix Epoch and labelled with the namespace name.

  • kube_applier_last_run_success - A Gauge that reports the results of the last run labelled with the namespace name.

  • kube_applier_run_queue - A Gauge that reports the number of runs that are currently queued, labelled with the namespace name and the run type.

  • kube_applier_run_queue_failures - A Counter that observes the number of times a run failed to queue properly, labelled with the namespace name and the run type.

  • kube_applier_waybill_spec_auto_apply - A Gauge that captures the value of autoApply in the Waybill spec, labelled with the namespace name.

  • kube_applier_waybill_spec_dry_run - A Gauge that captures the value of dryRun in the Waybill spec, labelled with the namespace name.

  • kube_applier_waybill_spec_run_interval - A Gauge that captures the value of runInterval in the Waybill spec, labelled with the namespace name.

The Prometheus HTTP API (also see the Go library) can be used for querying the metrics server.

Running locally

# manifests git repository
export LOCAL_REPO_PATH="${HOME}/dev/work/kubernetes-manifests"

# directory within the manifests repository that contains namespace directories
export CLUSTER_DIR="exp-1-aws"

export DIFF_URL_FORMAT="https://github.com/utilitywarehouse/kubernetes-manifests/commit/%s"

# export values for any other options that are configured through environment
# variables (the rest have default values and are optional) eg.:
export DRY_RUN="true"
export LOG_LEVEL="info"

make build
make run

Note that make run will mount and use ${HOME}/.kube for configuration, so ensure that your config files are using your intended context.

Running tests

Tests are written primarily using the envtest package of the controller-runtime project. Run make test to pull the required binary assets and run the tests. Once the assets are present in ./testbin you can invoke go test manually if you need a particular set of flags, but first you need to point envtest to the binaries: export KUBEBUILDER_ASSETS=$PWD/testbin/bin.

If you are writing tests, you might want to take a look at the tutorial, as well as the ginkgo and gomega documentation.

Releasing

Please use the make target "release" with "VERSION" argument to update all references and clean up after, example:

$ make release VERSION=v3.3.3-rc.3

Copyright and License

Copyright 2016 Box, Inc. All rights reserved.

Copyright (c) 2017-2024 Utility Warehouse Ltd.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.