ArgoCD Sync Wave + Postgres

The application

This project is composed by :

• vote : the voting application (a website in Nodejs)
• terraform : several terraform projects to manage the different stages of creation of the main project (reduce bash scripts and replace them with terraform code)
• manifests : the kubenetes templates
• argocd : the templates that define argocd applications

The voting application is defined with a few environment variables :

apiVersion: apps/v1
kind: Deployment
metadata:
  name: website
  namespace: vote-app
spec:
  selector:
    matchLabels:
      app: website
  replicas: 1
  template:
    metadata:
      labels:
        app: website
    spec:
      containers:
      - name: website
        image: ${website_image}
        env:
          - name: NODE_ENV
            value: production
          - name: VERSION
            value: "1.0.0"
          - name: WEBSITE_PORT
            value: "3000"
          - name: POSTGRES_USER
            value: "admin"
          - name: POSTGRES_HOST
            value: "postgres"
          - name: POSTGRES_DATABASE
            value: "vote"
          - name: POSTGRES_PASSWORD
            value: "password"
          - name: POSTGRES_PORT
            value: "5432"
        ports:
        - containerPort: 3000
      imagePullSecrets:
        - name: regcred

The application uses a Postgres database :

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres
  namespace: vote-app
spec:
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:14.3-alpine
          imagePullPolicy: Always
          ports:
            - name: tcp
              containerPort: 5432
          env:
            - name: POSTGRES_DB
              value: vote
            - name: POSTGRES_USER
              value: admin
            - name: POSTGRES_PASSWORD
              value: password

The database is configured and populated via a Job :

kind: ConfigMap
apiVersion: v1
metadata:
  name: postgres-script
  namespace: vote-app
data:
  SQL_SCRIPT: |-
    drop table if exists vote;
    --
    -- Create table `vote`
    --
    CREATE TABLE vote (
      name varchar(255),
      value integer
    );
    -- 
    -- Insert values into `vote`
    --
    INSERT INTO vote VALUES
    ('up', '0'),
    ('down', '0');
---
apiVersion: batch/v1
kind: Job
metadata:
  name: postgres-fill
  namespace: vote-app
  annotations:
    argocd.argoproj.io/hook: Sync
    argocd.argoproj.io/hook-delete-policy: HookSucceeded
spec:
  backoffLimit: 0
  ttlSecondsAfterFinished: 10
  template:
    spec:
      restartPolicy: Never
      volumes:
        - name: script
          configMap:
            name: postgres-script
            items:
              - key: SQL_SCRIPT
                path: SQL_SCRIPT_DUMP
      initContainers:
      - name: init-vote
        image: busybox:latest
        command: ['sh', '-c', 'until nc -vz postgres 5432 ; do sleep 1; done;']
      containers:
        - name: postgres-fill
          image: postgres:14.3-alpine
          volumeMounts:
            - name: script
              mountPath: '/script'
          env:
            - name: POSTGRES_DB
              value: vote
            - name: POSTGRES_USER
              value: admin
            - name: POSTGRES_PASSWORD
              value: password
            - name: POSTGRES_HOST
              value: "postgres"
            - name: SQL_SCRIPT
              valueFrom:
                configMapKeyRef:
                  name: postgres-script
                  key: SQL_SCRIPT
          command:
            - /bin/sh
          args:
            - -c
            - psql postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${POSTGRES_HOST}:5432/${POSTGRES_DB} --command="${SQL_SCRIPT}"

You can fork this repository

Important : make sure your repository is private as it will contain sensitive data !

Setup

The env-create script creates an .env file at the root of the project and installs stern if needed :

# create .env file + install stern
make env-create

You must modify the generated .env file with your own variables :

• AWS_REGION
• GITHUB_OWNER
• GITHUB_REPO
• GITHUB_TOKEN

You need to create a Github Token

You need to select repo :

You need to select admin:public_key :

This Github Token is used by Terraform’s github provider :

provider "github" {
  owner = var.github_owner
  token = var.github_token
}

To assign an SSH key to your Github account :

resource "github_user_ssh_key" "ssh_key" {
  title = var.project_name
  key   = tls_private_key.private_key.public_key_openssh
}

Let’s now initialize terraform projects :

# terraform init (updgrade) + validate
make terraform-init

Setup the infrastructure

# terraform create ecr repo + ssh key
make infra-create

Terraform is used to :

• Create an SSH key and add it to your Github account so you can interact with a private repository
• Create an ECR repository

Build and push the image to ECR

# build + push docker image to ecr
make build-ecr-push

Terraform is used to :

• Build and push the docker image

Start Kind, install ArgoCD + ArgoCD Image Updater

# setup kind + argocd + image updater
make kind-argocd-create

Terraform is used to :

• Start a Kind cluster
• Install and setup ArgoCD and Image Updater

kubectl get ns
NAME                 STATUS   AGE
argocd               Active   10s
default              Active   80s
kube-node-lease      Active   90s
kube-public          Active   90s
kube-system          Active   90s
local-path-storage   Active   70s

Create namespaces + secrets

# create namespaces + secrets
make secrets-create

Terraform is used to :

• Create namepsaces and secrets
• Namespaces are defined with these templates
• Secrets are defined with these templates

kubectl get secrets -n vote-app
NAME      TYPE                             DATA   AGE
regcred   kubernetes.io/dockerconfigjson   1      10s

Build manifest files from templates

# create files using templates
make templates-create

Terraform is used to :

• Build some files from templates
• Inject variables within ArgoCD applications
• Inject variables within deployements files

Important : generated files must be added to your git repository :

git add . && git commit -m update && git push -u origin master

We open the ArgoCD web interface :

# open argocd (website)
make argocd-open

Watch

Here are 4 useful ways to monitor logs and activity in our cluster

1. In a new terminal window run the command :

# watch logs using stern
make watch-logs

This command uses Stern, a very nice tool

stern . --namespace vote-app

Stern allows you to tail multiple pods on Kubernetes and multiple containers within the pod. Each result is color coded for quicker debugging.

2. In a new terminal window run the command :

# watch all within namespace
make watch-all

This command refresh each second you terminal to list all content within the vote-app namespace

3. In a new terminal window run the command :

# watch pods using kubectl
make watch-pods

This command uses the --watch option of kubectl. Only new states are displayed. No refresh of the complete display of the terminal. So it’s a useful history.

4. In a new terminal window run the command :

# watch events using kubectl
make watch-events

This command retrieve the events with kubectl with a combination of custom-columns. It’s practical and very detailed (sometimes too much).

kubectl get event \
    --output=custom-columns=TIME:.firstTimestamp,NAME:.metadata.name,REASON:.reason \
    --namespace vote-app \
    --watch

Deployment without sync

# create app (no sync)
make app-no-sync-create

We deploy the ArgoCD no-sync-wave application

The application deploys the manifests contained in the manifests/no-sync folder

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: no-sync-wave
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
  annotations:
    argocd-image-updater.argoproj.io/image-list: website=${website_image}
    argocd-image-updater.argoproj.io/website.pull-secret: secret:argocd/aws-ecr-creds#creds
    argocd-image-updater.argoproj.io/write-back-method: git:secret:argocd/git-creds
spec:
  project: default

  source:
    repoURL: ${git_repo_url}
    targetRevision: HEAD
    path: manifests/no-sync
  destination: 
    server: https://kubernetes.default.svc
    namespace: default

Important : if you use Job / CronJob + ttlSecondsAfterFinished with ArgoCD, ArgoCD will instantly recreate the job.

Because the desired state differs from the new current state (ArgoCD ignore your ttlSecondsAfterFinished declaration)

To resolve this use the annotations : hook: Sync + hook-delete-policy: HookSucceeded

annotations:
    argocd.argoproj.io/hook: Sync
    argocd.argoproj.io/hook-delete-policy: HookSucceeded

Hooks are simply Kubernetes manifests tracked in the source repository of your Argo CD Application using the annotation hook

• hook: Sync : Executes after all PreSync hooks completed and were successful, at the same time as the application of the manifests

Hooks can be deleted in an automatic fashion using the annotation hook-delete-policy

• hook-delete-policy: HookSucceeded : The hook resource is deleted after the hook succeeded (e.g. Job/Workflow completed successfully)

By analyzing the logs in the different terminals, we will see :

• The website pod is running before postgres pod :

• The logs show connection errors :

• The log history shows the number of failed tries :

postgres-5cb5b9584d-psnc8   0/1     Pending   0          0s
website-85984b8d5d-jbv6z    0/1     Pending   0          0s
postgres-5cb5b9584d-psnc8   0/1     Pending   0          0s
website-85984b8d5d-jbv6z    0/1     Pending   0          0s
postgres-5cb5b9584d-psnc8   0/1     ContainerCreating   0          0s
website-85984b8d5d-jbv6z    0/1     ContainerCreating   0          1s
postgres-fill-9vz9k         0/1     Pending             0          0s
postgres-fill-9vz9k         0/1     Pending             0          0s
postgres-fill-9vz9k         0/1     Init:0/1            0          0s
website-85984b8d5d-jbv6z    1/1     Running             0          36s
website-85984b8d5d-jbv6z    0/1     Error               0          57s
website-85984b8d5d-jbv6z    1/1     Running             1 (23s ago)   59s
website-85984b8d5d-jbv6z    0/1     Error               1 (25s ago)   61s
website-85984b8d5d-jbv6z    0/1     CrashLoopBackOff    1 (13s ago)   72s
website-85984b8d5d-jbv6z    1/1     Running             2 (14s ago)   73s
website-85984b8d5d-jbv6z    0/1     Error               2 (17s ago)   76s
postgres-5cb5b9584d-psnc8   1/1     Running             0             84s
website-85984b8d5d-jbv6z    0/1     CrashLoopBackOff    2 (18s ago)   92s
postgres-fill-9vz9k         0/1     Init:0/1            0             97s
website-85984b8d5d-jbv6z    1/1     Running             3 (37s ago)   111s
website-85984b8d5d-jbv6z    0/1     Error               3 (46s ago)   2m
postgres-fill-9vz9k         0/1     PodInitializing     0             2m2s
postgres-fill-9vz9k         1/1     Running             0             2m3s
postgres-fill-9vz9k         0/1     Completed           0             2m4s
postgres-fill-9vz9k         0/1     Completed           0             2m7s
postgres-fill-9vz9k         0/1     Completed           0             2m8s
postgres-fill-9vz9k         0/1     Terminating         0             2m9s
postgres-fill-9vz9k         0/1     Terminating         0             2m10s
website-85984b8d5d-jbv6z    0/1     CrashLoopBackOff    3 (21s ago)   2m12s
website-85984b8d5d-jbv6z    1/1     Running             4 (47s ago)   2m38s

We remove the application by running this command :

# destroy app (no sync)
make app-no-sync-destroy

Deployment with Sync Wave

ArgoCD Sync Waves are defined by the following annotation :

metadata:
  annotations:
    argocd.argoproj.io/sync-wave: "5"

Default value is 0. A wave can be negative

Each wave represents a step to complete before moving on to the next wave (lowest values first)

Within a wave, the resources are executed in this order : namespaces then the other resources …

The current delay between each sync wave is 2 seconds

Exhaustive ArgoCD Sync Waves documentation

# create app (no sync)
make app-sync-create

We deploy the ArgoCD Sync Wave application

The application deploys the manifests contained in the manifests/sync folder

Here are some interesting steps defined for the deployment of our application :

1. sync-wave: "0" : Postgres database deployment

2. sync-wave: "1" : Creation of a ConfigMap containing the SQL script

3. sync-wave: "1" : Job to create the schema and seed the database

4. sync-wave: "2" : Deploying the Node app

By analyzing the logs in the different terminals, we will see :

• The website pod is waiting the postgres + postgres-fill pods :

• The logs show no errors and a fast and clean execution :

• The log history shows fast and clean steps :

make watch-pods
NAME                        READY   STATUS    RESTARTS   AGE
postgres-5cb5b9584d-dz9m9   0/1     Pending   0          0s
postgres-5cb5b9584d-dz9m9   0/1     Pending   0          0s
postgres-5cb5b9584d-dz9m9   0/1     ContainerCreating   0          0s
postgres-5cb5b9584d-dz9m9   1/1     Running             0          4s
postgres-fill-925b5         0/1     Pending             0          0s
postgres-fill-925b5         0/1     Pending             0          0s
postgres-fill-925b5         0/1     Init:0/1            0          1s
postgres-fill-925b5         0/1     Init:0/1            0          8s
postgres-fill-925b5         0/1     PodInitializing     0          13s
postgres-fill-925b5         1/1     Running             0          14s
postgres-fill-925b5         0/1     Completed           0          15s
postgres-fill-925b5         0/1     Completed           0          17s
postgres-fill-925b5         0/1     Completed           0          18s
website-85984b8d5d-hrtx7    0/1     Pending             0          0s
website-85984b8d5d-hrtx7    0/1     Pending             0          0s
website-85984b8d5d-hrtx7    0/1     ContainerCreating   0          1s
postgres-fill-925b5         0/1     Terminating         0          22s
postgres-fill-925b5         0/1     Terminating         0          22s
website-85984b8d5d-hrtx7    1/1     Running             0          4s

We open our browser on http://0.0.0.0:9000/ :

Cleaning

This demonstration is now over, we are destroying the resources :

# terraform destroy kind + argocd
make kind-argocd-destroy

# terraform destroy ecr repo + ssh key
make infra-destroy