OpenFaaS GitOps workflow with Flux and Helm v3

This is a step-by-step guide on how to set up a GitOps workflow for OpenFaaS with Flux CD and its Helm Operator. GitOps is a way to do Continuous Delivery, it works by using Git as a source of truth for declarative infrastructure and workloads. In practice this means using git push instead of kubectl apply/delete or helm install/upgrade.

OpenFaaS is an open source function-as-a-service platform for Kubernetes. With OpenFaaS you can package your code or an existing binary in a Docker image to get a highly scalable endpoint with auto-scaling and metrics.

Flux is a GitOps operator for Kubernetes that keeps your cluster state is sync with a Git repository. Because Flux is pull based and also runs inside Kubernetes, you don't have to expose the cluster credentials outside your production environment. Once you enable Flux on your cluster any changes in your production environment are done via pull request with rollback and audit logs provided by Git.

You can define the desired state of your cluster with Helm charts, Kubernetes deployments, network policies and even custom resources like OpenFaaS functions or sealed secrets. Flux implements a control loop that continuously applies the desired state to your cluster, offering protection against harmful actions like deployments deletion or policies altering.

Prerequisites

You'll need a Kubernetes cluster v1.11 or newer with load balancer support, a GitHub account, git and kubectl installed locally.

On GitHub, fork the openfaas-flux repository and clone it locally (replace stefanprodan with your GitHub username):

git clone https://github.com/stefanprodan/openfaas-flux
cd openfaas-flux

Install Helm v3 and fluxctl for macOS with Homebrew:

brew install helm fluxctl

On Windows you can use Chocolatey:

choco install kubernetes-helm fluxctl

Install Flux and Helm Operator

Add FluxCD repository to Helm repos:

helm repo add fluxcd https://charts.fluxcd.io

Create the fluxcd namespace:

kubectl create ns fluxcd

Install Flux by specifying your fork URL (replace stefanprodan with your GitHub username):

helm upgrade -i flux fluxcd/flux --wait \
--namespace fluxcd \
--set [email protected]:stefanprodan/openfaas-flux 

Install the HelmRelease Kubernetes custom resource definition:

kubectl apply -f https://raw.githubusercontent.com/fluxcd/helm-operator/master/deploy/flux-helm-release-crd.yaml

Install Flux Helm Operator with Helm v3 support:

helm upgrade -i helm-operator fluxcd/helm-operator --wait \
--namespace fluxcd \
--set git.ssh.secretName=flux-git-deploy \
--set helm.versions=v3

Setup Git sync

At startup, Flux generates a SSH key and logs the public key. Find the public key with:

fluxctl identity --k8s-fwd-ns fluxcd

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 repository, go to Settings > Deploy keys click on Add deploy key, check Allow write access, paste the Flux public key and click Add key.

After a couple of seconds Flux will create the openfaas and openfaas-fn namespaces and will install the OpenFaaS Helm release.

Check the OpenFaaS deployment status:

watch kubectl -n openfaas get helmrelease openfaas

Manage Helm releases with Flux

The Helm operator provides an extension to Flux that automates Helm chart releases. 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 Helm operator makes sure Helm charts are released as specified in the resources.

Let's take a look at the OpenFaaS definition by running cat ./releases/openfaas.yaml inside the git repo:

apiVersion: helm.fluxcd.io/v1
kind: HelmRelease
metadata:
  name: openfaas
  namespace: openfaas
spec:
  releaseName: openfaas
  chart:
    repository: https://openfaas.github.io/faas-netes/
    name: openfaas
    version: 5.4.0
  values:
    generateBasicAuth: true
    exposeServices: false
    serviceType: LoadBalancer
    operator:
      create: true

The spec.chart section tells Flux Helm Operator where is the chart repository and what version to install. The spec.values are user customizations of default parameter values from the chart itself. Changing the version or a value in git, will make the Helm Operator upgrade the release.

Edit the release and set two replicas for the queue worker with:

cat << EOF | tee releases/openfaas.yaml
apiVersion: helm.fluxcd.io/v1
kind: HelmRelease
metadata:
  name: openfaas
  namespace: openfaas
spec:
  releaseName: openfaas
  chart:
    repository: https://openfaas.github.io/faas-netes/
    name: openfaas
    version: 5.4.0
  values:
    generateBasicAuth: true
    serviceType: LoadBalancer
    operator:
      create: true
    queueWorker:
      replicas: 2
EOF

A list of all supported chart values can be found in the faas-netes repo.

Apply changes via git:

git add -A && \
git commit -m "scale up queue worker" && \
git push origin master && \
fluxctl sync --k8s-fwd-ns fluxcd

Note that Flux does a git-cluster reconciliation every five minutes, the fluxctl sync command can be used to speed up the synchronization.

Check that Helm Operator has upgraded the release and that the queue worker was scaled up:

watch kubectl -n openfaas get pods

Retrieve the OpenFaaS credentials with:

PASSWORD=$(kubectl -n openfaas get secret basic-auth -o jsonpath="{.data.basic-auth-password}" | base64 --decode) && \
echo "OpenFaaS admin password: $PASSWORD"

Find the OpenFaaS gateway load balancer address with:

kubectl -n openfaas get svc gateway-external -o wide

Navigate to the gateway address on port 8080 in your browser and login with the admin user and the password retrieved earlier.

Manage OpenFaaS functions with Flux

An OpenFaaS function is described through a Kubernetes custom resource named function. The Flux daemon synchronizes these resources from git to the cluster, and the OpenFaaS Operator creates for each function a Kubernetes deployment and a ClusterIP service as specified in the resources.

You'll use a Helm chart stored in git to bundle multiple functions and manage the install and upgrade process.

The functions chart contains two function manifests, certinfo and podinfo:

./functions/
├── Chart.yaml
├── templates
│   ├── certinfo.yaml
│   └── podinfo.yaml
└── values.yaml

You can add. modify or remove functions in the functions/templates dir and Flux Helm Operator will create, update or delete functions in your cluster according to the changes pushed to the master branch.

Install the chart by setting fluxcd.io/ignore: "false" (replace stefanprodan with your GitHub username):

cat << EOF | tee releases/functions.yaml
apiVersion: helm.fluxcd.io/v1
kind: HelmRelease
metadata:
  name: functions
  namespace: openfaas-fn
  annotations:
    fluxcd.io/ignore: "false"
spec:
  releaseName: functions
  chart:
    git: [email protected]:stefanprodan/openfaas-flux
    ref: master
    path: functions
EOF

The above manifest instructs Helm Operator to clone the git repository using Flux SSH key and install or upgrade the functions chart in the openfaas-fn namespace.

Apply changes via git:

git add -A && \
git commit -m "install functions" && \
git push origin master && \
fluxctl sync --k8s-fwd-ns fluxcd

List the installed functions with:

kubectl -n openfaas-fn get functions

Invoke the certinfo function with:

curl -d "openfaas.com" http://<GATEWAY_ADDRESS>:8080/function/certinfo

Automate OpenFaaS functions updates

Flux can be used to automate container image updates in your cluster. Flux periodically scans the pods running in your cluster and builds a list of all container images. Using the image pull secrets, it connects to the container registries, pulls the images metadata and stores the image tag list in memcached.

You can enable the automate image tag updates by annotating your HelmReleases objects. You can also control what tags should be considered for an update by using glob, regex or semantic version expressions.

Edit the functions release and add container image update policies for the OpenFaaS functions (replace stefanprodan with your GitHub username):

cat << EOF | tee releases/functions.yaml
apiVersion: helm.fluxcd.io/v1
kind: HelmRelease
metadata:
  name: functions
  namespace: openfaas-fn
  annotations:
    fluxcd.io/automated: "true"
    filter.fluxcd.io/certinfo: semver:~1.0
    filter.fluxcd.io/podinfo: semver:~3.1
spec:
  releaseName: functions
  chart:
    git: [email protected]:stefanprodan/openfaas-flux
    ref: master
    path: functions
  values:
    certinfo:
      image: stefanprodan/certinfo:1.0.0
    podinfo:
      image: stefanprodan/podinfo:3.1.0
EOF

The above annotations tell Flux to update the Helm release values.<function>.image every time a new image is pushed to Docker Hub with a tag that matches the semver filter. Note that Flux only works with immutable image tags (:latest is not supported). Every image tag must be unique, for this you can use the Git commit SHA or semver when tagging images.

Apply the update policies via git:

git add -A && \
git commit -m "enable functions updates" && \
git push origin master && \
fluxctl sync --k8s-fwd-ns fluxcd

Once the automation is enabled, Flux will apply the semver filter and update the functions images in git and in the cluster:

Verify that podinfo version has been updated:

$ curl -s http://<GATEWAY_ADDRESS>:8080/function/podinfo/api/info | grep version

"version": "3.1.5"

Encrypt Kubernetes secrets in git

In order to store secrets safely in a public Git repo you can use the 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 controller has been installed by Flux in the fluxcd namespace, the Helm release can be found in releases/sealed-secrets.yaml.

Install the kubeseal CLI:

brew install 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

Generate a Kubernetes secret locally with kubectl:

kubectl create secret generic db-credentials \
--from-literal=user=my-db-user \
--from-literal=password=my-db-pass \
--dry-run \
-o json > db-credentials.json

Encrypt the secret with kubeseal and add it to the functions chart:

kubeseal --format=yaml --cert=pub-cert.pem \
< db-credentials.json > functions/templates/db-credentials.yaml

Edit certinfo and add the secret to the function definition:

cat << EOF | tee functions/templates/certinfo.yaml
apiVersion: openfaas.com/v1alpha2
kind: Function
metadata:
  name: certinfo
  labels:
{{ include "functions.labels" . | indent 4 }}
spec:
  name: certinfo
  image: {{ .Values.certinfo.image }}
  readOnlyRootFilesystem: true
  secrets:
    - db-credentials
EOF

The above configuration instructs the OpenFaaS operator to mount the db-credentials secret as a file inside the function container at /var/openfaas/secrets/.

Delete the plain text secret and apply changes via git:

rm db-credentials.json && \
git add -A && \
git commit -m "add db credentials" && \
git push origin master && \
fluxctl sync --k8s-fwd-ns fluxcd

Flux will apply the sealed secret on your cluster and sealed-secrets controller will then decrypt it into a Kubernetes secret.

You can read more about secrets management on the OpenFaaS docs website.

Developer workflow

You'll be using the OpenFaaS CLI to create functions, build and push them to a container registry.

Install faas-cli and login to your instance:

curl -sL https://cli.openfaas.com | sudo sh

echo $PASSWORD | faas-cli login -u admin --password-stdin \
--gateway http://<GATEWAY_ADDRESS>:8080

Create a function using the Go template (replace stefanprodan with your Docker Hub username):

faas-cli new myfn --lang go --prefix stefanprodan

Implement your function logic by editing the myfn/handler.go file.

Initialize a Git repository for your function and commit your changes:

git init
git add . && git commit -s -m "Init function"

Build the container image by tagging it with the Git branch and commit short SHA:

$ faas-cli build --tag branch -f myfn.yml

Image: stefanprodan/myfn:latest-master-eb656a6 built.

Push the image to Docker Hub with:

$ faas-cli push --tag branch -f myfn.yml

Pushing myfn [stefanprodan/myfn:latest-master-eb656a6] done.

Generate the function Kubernetes custom resource with:

faas-cli generate -n "" --tag branch --yaml myfn.yml > myfn-k8s.yaml

Edit the generated YAML so that Flux can use Helm to control the version and labels:

cat << EOF | tee functions/templates/myfn.yaml
apiVersion: openfaas.com/v1alpha2
kind: Function
metadata:
  name: myfn
  labels:
{{ include "functions.labels" . | indent 4 }}
spec:
  name: myfn
  image: {{ .Values.myfn.image }}
EOF

Add your function container image to the chart values.yaml:

cat << EOF | tee functions/values.yaml
certinfo:
  image: stefanprodan/certinfo:1.0.0
podinfo:
  image: stefanprodan/podinfo:3.1.0
myfn:
  image: stefanprodan/myfn:latest-master-eb656a6
EOF

Add your function to the Helm release and set a Flux filter using a glob expression:

cat << EOF | tee releases/functions.yaml
apiVersion: helm.fluxcd.io/v1
kind: HelmRelease
metadata:
  name: functions
  namespace: openfaas-fn
  annotations:
    fluxcd.io/automated: "true"
    filter.fluxcd.io/certinfo: semver:~1.0
    filter.fluxcd.io/podinfo: semver:~3.1
    filter.fluxcd.io/myfn: glob:latest-master-*
spec:
  releaseName: functions
  chart:
    git: [email protected]:stefanprodan/openfaas-flux
    ref: master
    path: functions
  values:
    certinfo:
      image: stefanprodan/certinfo:1.0.0
    podinfo:
      image: stefanprodan/podinfo:3.1.0
    myfn:
      image: stefanprodan/myfn:latest-master-eb656a6
EOF

To automate the whole process you can use the OpenFaaS GitHub action to run faas-cli build and push on every commit to the master branch. Flux will detect master builds and will deploy the new images to your cluster.