GitOps is a way to do Continuous Delivery, it works by using Git as a source of truth for declarative infrastructure and workloads. For Kubernetes this means using git push instead of kubectl create/apply or helm install/upgrade.
In a traditional CICD pipeline, CD is an implementation extension powered by the continuous integration tooling to promote build artifacts to production. In the GitOps pipeline model, any change to production must be committed in source control (preferable via a pull request) prior to being applied on the cluster. This way rollback and audit logs are provided by Git. If the entire production state is under version control and described in a single Git repository, when disaster strikes, the whole infrastructure can be quickly restored from that repository.
To better understand the benefits of this approach to CD and what the differences between GitOps and Infrastructure-as-Code tools are, head to the Weaveworks website and read What is GitOps really? .
In order to apply the GitOps pipeline model to Kubernetes you need three things:
a Git repository with your workloads definitions in YAML format, Helm charts and any other Kubernetes custom resource that defines your cluster desired state (I will refer to this as the config repository)
a container registry where your CI system pushes immutable images (no latest tags, use semantic versioning or git commit sha)
an operator that runs in your cluster and does a two-way synchronization:
watches the registry for new image releases and based on deployment policies updates the workload definitions with the new image tag and commits the changes to the config repository
watches for changes in the config repository and applies them to your cluster
I will be using Google Cloud Kubernetes managed service to run the workloads, GitHub to host the config repo, Docker Hub as the container registry and Weave Flux OSS as the GitOps Kubernetes Operator.
Install Helm and Tiller
If you don’t have Helm CLI installed, on macOS you can use brew install kubernetes-helm.
Create a service account and a cluster role binding for Tiller:
kubectl -n kube-system create sa tiller kubectl create clusterrolebinding tiller-cluster-rule \ --clusterrole=cluster-admin \ --serviceaccount=kube-system:tiller
Note that on GKE you need to create an admin cluster user for yourself:
kubectl create clusterrolebinding "cluster-admin-$(whoami)" \ --clusterrole=cluster-admin \ --user="$(gcloud config get-value core/account)"
Deploy Tiller in kube-system namespace:
helm init --skip-refresh --upgrade --service-account tiller
Install Weave Flux
The first step in automating Helm releases with Weave Flux is to create a Git repository with your charts source code. You can fork the gitops-helm project and use it as a template for your cluster config.
After you fork th repo, update the release definitions with your Docker Hub repository and GitHub username located in \releases\(dev/stg/prod)\podinfo.yaml in your master branch before proceeding.
Add the Weave Flux chart repo:
helm repo add weaveworks https://weaveworks.github.io/flux
Install Weave Flux and its Helm Operator by specifying your fork URL (replace stefanprodan with your GitHub username):
helm install --name flux \ --set rbac.create=true \ --set helmOperator.create=true \ --set git.url=ssh://email@example.com/stefanprodan/gitops-helm \ --namespace flux \ weaveworks/flux
The Flux Helm operator provides an extension to Weave Flux that automates Helm Chart releases for it. A Chart release is described through a Kubernetes custom resource named HelmRelease. The Flux daemon synchronizes these resources from git to the cluster, and the Flux Helm operator makes sure Helm charts are released as specified in the resources.
Note that Flux Helm Operator works with Kubernetes 1.9 or newer.
At startup Flux generates a SSH key and logs the public key. Find the SSH public key with:
kubectl -n flux logs deployment/flux | grep identity.pub | cut -d '"' -f2
In order to sync your cluster state with Git you need to copy the public key and create a deploy key with write access on your GitHub repository.
Open GitHub, navigate to your fork, go to Setting > Deploy keys click on Add deploy key, check Allow write access, paste the Flux public key and click Add key.
GitOps pipeline example
The config repo has the following structure:
├── charts │ └── podinfo │ ├── Chart.yaml │ ├── README.md │ ├── templates │ └── values.yaml ├── hack │ ├── Dockerfile.ci │ └── ci-mock.sh ├── namespaces │ ├── dev.yaml │ └── stg.yaml └── releases ├── dev │ └── podinfo.yaml └── stg └── podinfo.yaml
I will be using podinfo to demonstrate a full CI/CD pipeline including promoting releases between environments.
I’m assuming the following Git branching model:
dev branch (feature-ready state)
stg branch (release-candidate state)
master branch (production-ready state)
When a PR is merged in the dev or stg branch will produce a immutable container image as in repo/app:branch-commitsha.
Inside the hack dir you can find a script that simulates the CI process for dev and stg. The ci-mock.sh script does the following:
pulls the podinfo source code from GitHub
generates a random string and modifies the code
generates a random Git commit short SHA
builds a Docker image with the format: yourname/podinfo:branch-sha
pushes the image to Docker Hub
Let’s create an image corresponding to the dev branch (replace stefanprodan with your Docker Hub username):
$ cd hack && ./ci-mock.sh -r stefanprodan/podinfo -b dev Sending build context to Docker daemon 4.096kB Step 1/15 : FROM golang:1.10 as builder .... Step 9/15 : FROM alpine:3.7 .... Step 12/15 : COPY --from=builder /go/src/github.com/stefanprodan/k8s-podinfo/podinfo . .... Step 15/15 : CMD ["./podinfo"] .... Successfully built 71bee4549fb2 Successfully tagged stefanprodan/podinfo:dev-kb9lm91e The push refers to repository [docker.io/stefanprodan/podinfo] 36ced78d2ca2: Pushed
Inside the charts directory there is a podinfo Helm chart. Using this chart I want to create a release in the dev namespace with the image I've just published to Docker Hub. Instead of editing the values.yaml from the chart source I will create a FluxHelmRelease definition:
apiVersion: flux.weave.works/v1beta1 kind: HelmRelease metadata: name: podinfo-dev namespace: dev annotations: flux.weave.works/automated: "true" flux.weave.works/tag.chart-image: glob:dev-* spec: releaseName: podinfo-dev chart: git: firstname.lastname@example.org:stefanprodan/gitops-helm path: charts/podinfo ref: master values: image: stefanprodan/podinfo:dev-kb9lm91e replicaCount: 1
Flux Helm release fields:
metadata.name is mandatory and needs to follow Kubernetes naming conventions
metadata.namespace is optional and determines where the release is created
spec.releaseName is optional and if not provided the release name will be $namespace-$name
spec.chart.path is the directory containing the chart, given relative to the repo root
spec.values are user customizations of default parameter values from the chart itself
The options specified in the FluxHelmRelease spec.values will override the ones in values.yaml from the chart source.
With the flux.weave.works annotations I instruct Flux to automate this release. When a new tag with the prefix dev is pushed to Docker Hub, Flux will update the image field in the yaml file, will commit and push the change to Git and finally will apply the change on the cluster.
When the podinfo-dev FluxHelmRelease object changes inside the cluster, Kubernetes API will notify the Flux Helm Operator and the operator will perform a Helm release upgrade.
$ helm history podinfo-dev REVISION STATUS CHART 1 SUPERSEDED podinfo-0.2.0 Install complete 2 DEPLOYED podinfo-0.2.0 Upgrade complete
The Flux Helm Operator reacts to changes in the HelmRelease collection but will also detect changes in the charts source files. If I make a change to the podinfo chart, the operator will pick that up and run an upgrade.
$ helm history podinfo-dev REVISION STATUS CHART DESCRIPTION 1 SUPERSEDED podinfo-0.2.0 Install complete 2 SUPERSEDED podinfo-0.2.0 Upgrade complete 3 DEPLOYED podinfo-0.2.1 Upgrade complete
Now let’s assume that I want to promote the code from the dev branch into a more stable environment for others to test it. I would create a release candidate by merging the podinfo code from dev into the stg branch. The CI would kick in and publish a new image:
$ cd hack && ./ci-mock.sh -r stefanprodan/podinfo -b stg Successfully tagged stefanprodan/podinfo:stg-9ij63o4c The push refers to repository [docker.io/stefanprodan/podinfo] 8f21c3669055: Pushed
Assuming the staging environment has some sort of automated load testing in place, I want to have a different configuration than dev:
apiVersion: flux.weave.works/v1beta1 kind: HelmRelease metadata: name: podinfo-rc namespace: stg annotations: flux.weave.works/automated: "true" flux.weave.works/tag.chart-image: glob:stg-* spec: releaseName: podinfo-rc chart: git: email@example.com:stefanprodan/gitops-helm path: charts/podinfo ref: master values: image: stefanprodan/podinfo:stg-9ij63o4c replicaCount: 2 hpa: enabled: true maxReplicas: 10 cpu: 50 memory: 128Mi
With Flux Helm releases it’s easy to manage different configurations per environment. When adding a new option in the chart source make sure it’s turned off by default so it will not affect all environments.
If I want to create a new environment, let’s say for hotfixes testing, I would do the following:
create a new namespace definition in namespaces/hotfix.yaml
create a dir releases/hotfix
create a FluxHelmRelease named podinfo-hotfix
set the automation filter to glob:hotfix-*
make the CI tooling publish images from my hotfix branch to stefanprodan/podinfo:hotfix-sha
Production promotions with sem ver
For production, instead of tagging the images with the Git commit, I will use Semantic Versioning.
Let’s assume that I want to promote the code from the stg branch into master and do a production release. After merging stg into master via a pull request, I would cut a release by tagging master with version 0.4.10.
When I push the git tag, the CI will publish a new image in the repo/app:git_tag format:
$ cd hack && ./ci-mock.sh -r stefanprodan/podinfo -v 0.4.10 Successfully built f176482168f8 Successfully tagged stefanprodan/podinfo:0.4.10
If I want to automate the production deployment based on version tags, I would use semver filters instead of glob:
apiVersion: flux.weave.works/v1beta1 kind: HelmRelease metadata: name: podinfo-prod namespace: prod annotations: flux.weave.works/automated: "true" flux.weave.works/tag.chart-image: semver:~0.4 spec: releaseName: podinfo-prod chart: git: firstname.lastname@example.org:stefanprodan/gitops-helm path: charts/podinfo ref: master values: image: stefanprodan/podinfo:0.4.10 replicaCount: 3
Now if I release a new patch, let’s say 0.4.11, Flux will automatically deploy it.
$ cd hack && ./ci-mock.sh -r stefanprodan/podinfo -v 0.4.11 Successfully tagged stefanprodan/podinfo:0.4.11
Managing Kubernetes secrets
In order to store secrets safely in a public Git repo you can use the Bitnami Sealed Secrets controller and encrypt your Kubernetes Secrets into SealedSecrets. The SealedSecret can be decrypted only by the controller running in your cluster.
The Sealed Secrets Helm chart is available on Helm Hub, so I can use the Helm repository instead of a git repo. This is the sealed-secrets controller release:
apiVersion: flux.weave.works/v1beta1 kind: HelmRelease metadata: name: sealed-secrets namespace: adm annotations: flux.weave.works/automated: "false" spec: releaseName: sealed-secrets chart: repository: https://kubernetes-charts.storage.googleapis.com/ name: sealed-secrets version: 1.0.1 values: image: repository: quay.io/bitnami/sealed-secrets-controller tag: v0.7.0
Note that this release is not automated, since this is a critical component I prefer to update it manually.
Install the kubeseal CLI:
sudo install -m 755 kubeseal-darwin-amd64 /usr/local/bin/kubeseal
At startup, the sealed-secrets controller generates a RSA key and logs the public key. Using kubeseal you can save your public key as pub-cert.pem, the public key can be safely stored in Git, and can be used to encrypt secrets without direct access to the Kubernetes cluster:
kubeseal --fetch-cert \ --controller-namespace=adm \ --controller-name=sealed-secrets \ > pub-cert.pem
You can generate a Kubernetes secret locally with kubectl and encrypt it with kubeseal:
kubectl -n dev create secret generic basic-auth \ --from-literal=user=admin \ --from-literal=password=admin \ --dry-run \ -o json > basic-auth.json kubeseal --format=yaml --cert=pub-cert.pem < basic-auth.json > basic-auth.yaml
This generates a custom resource of type SealedSecret that contains the encrypted credentials:
apiVersion: bitnami.com/v1alpha1 kind: SealedSecret metadata: name: basic-auth namespace: adm spec: encryptedData: password: AgAR5nzhX2TkJ....... user: AgAQDO58WniIV3gTk.......
Delete the basic-auth.json file and push the pub-cert.pem and basic-auth.yaml to Git:
rm basic-auth.json mv basic-auth.yaml /releases/dev/ git commit -a -m "Add basic auth credentials to dev namespace" && git push
Flux will apply the sealed secret on your cluster and sealed-secrets controller will then decrypt it into a Kubernetes secret.
To prepare for disaster recovery you should backup the sealed-secrets controller private key with:
kubectl get secret -n adm sealed-secrets-key -o yaml --export > sealed-secrets-key.yaml
To restore from backup after a disaster, replace the newly-created secret and restart the controller:
kubectl replace secret -n adm sealed-secrets-key -f sealed-secrets-key.yaml kubectl delete pod -n adm -l app=sealed-secrets
Flux Helm Integration FAQ
My Helm charts have more than one container image. How can I automate the image tag update for all my containers?
A container image list must have the following format:
container_name_1: image: repo/app1:tag container_name_2: image: quay.io/repo/app2:tag
Here is an example with different deployment automation policies:
apiVersion: flux.weave.works/v1beta1 kind: HelmRelease metadata: name: openfaas namespace: openfaas annotations: flux.weave.works/automated: "true" flux.weave.works/tag.prometheus: semver:~2.3 flux.weave.works/tag.alertmanager: glob:v0.15.* flux.weave.works/tag.nats: regexp:^0.6.* spec: releaseName: openfaas chart: repository: https://openfaas.github.io/faas-netes/ name: openfaas version: 1.3.3 values: prometheus: image: prom/prometheus:v2.3.1 alertmanager: image: prom/alertmanager:v0.15.0 nats: image: nats-streaming:0.6.0
I’m using SSL between Helm and Tiller. How can I configure Flux to use the certificate?
When installing Flux, you can supply the CA and client-side certificate using the helmOperator.tls options, more details here.
I’ve deleted a HelmRelease file from Git. Why is the Helm release still running on my cluster?
Flux doesn’t delete resources, there is an issue opened about this topic on GitHub. In order to delete a Helm release first remove the file from Git and afterwards run:
kubectl -n dev delete helmrelease/podinfo-dev
The Flux Helm operator will receive the delete event and will purge the Helm release.
I’ve uninstalled Flux and all my Helm releases are gone. Why is that?
On HelmRelease CRD deletion, Kubernetes will remove all HelmRelease CRs triggering a Helm purge for each release created by Flux. To avoid this you have to manually delete the Flux Helm Operator with kubectl -n flux delete deployment/flux-helm-operator before running helm delete flux.
I have a dedicated Kubernetes cluster per environment and I want to use the same Git repo for all. How can I do that?
For each cluster create a Git branch in your config repo. When installing Flux set the Git branch using --set git.branch=cluster-name.
How can I monitor the CD pipeline and the workloads managed by Flux?
Weave Cloud is a SaaS product by Weaveworks that extends Flux with:
a UI for all Flux operations, audit trail and alerts for deployments
a realtime map of your cluster to debug and analyse its state
full observability and insights into your cluster (hosted Prometheus with 13 months of metrics history)
instant Flux operations via GitHub webhooks routing
Originally published at www.weave.works.