How to run the server in Kubernetes?

Service

First we deploy the K8s service of type ClusterIP that only allows communication inside the cluster. As we are running a database server it would typically serve other backends in the same cluster and not be accessible from the outside. If such access is needed consider using LoadBalancer type service or Ingress controller with the ClusterIp service. The port available in the cluster is 3000 under a name of agdb. Furthermore we specify selector value app: agdb and also a label of the same value.

apiVersion: v1
kind: Service
metadata:
    name: agdb
    labels:
        app: agdb
spec:
    ports:
        - port: 3000
          name: agdb
    clusterIP: None
    selector:
        app: agdb

Secret

Next document is the pepper secret agdb-pepper.

apiVersion: v1
kind: Secret
metadata:
    name: agdb-pepper
    labels:
        app: agdb
stringData:
    pepper: "1234567891234567"

ConfigMap

The configuration named agdb-config via the ConfigMap is optional as the default configuration would work just as well. It might however be useful if you needed to change anything regarding the server later.

---
apiVersion: v1
kind: ConfigMap
metadata:
    name: agdb-config
    labels:
        app: agdb
data:
    agdb_server.yaml: |
        bind: :::3000
        address: http://agdb.default.svc.cluster.local:3000
        basepath: ""
        admin: admin
        log_level: INFO
        data_dir: /agdb/data
        pepper_path: /agdb/pepper/pepper
        cluster_token: cluster
        cluster_heartbeat_timeout_ms: 1000
        cluster_term_timeout_ms: 3000
        cluster: []

StatefulSet

The main part of the deployment is the stateful set definition. While replica set could work to some extent the instances of agdb_server are not interchangable and cannot be freely scaled horizontally. The stateful set type is therefore a better fit. It uses the selector and labels app: agdb in order to “link” the service and the underlying pod together. Kubernetes is using selectors rather than direct mapping when linking various things together such as services and pods. We specify 1 replica only (refer to the agdb as K8s cluster for an alternative).

The container spec matches the port on the service by name agdb and exposes the container port 3000 (default). The security context specifies the user 1000 (default uid in the container) and disables root access as it is not needed and enhances security.

Finally we specify volumes and volume mounts to add the secret, configmap and persistent volume claim (PVC) to the expected locations. The PVC is a way how data can survive restart or redeployment. By default 1 GB of storage is specified which can be increased (but not decreased) in subsequent deployments.

---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: agdb
  labels:
    app: agdb
spec:
  serviceName: "agdb"
  replicas: 1
  selector:
    matchLabels:
      app: agdb
  template:
    metadata:
      labels:
        app: agdb
    spec:
      containers:
        - name: agdb
          image: agnesoft/agdb:dev
          ports:
            - containerPort: 3000
              name: agdb
          securityContext:
            runAsUser: 1000
            runAsGroup: 1000
          securityContext:
            allowPrivilegeEscalation: false
          volumeMounts:
            - name: agdb-data
              mountPath: /agdb/data
            - name: config
              mountPath: /agdb
            - name: pepper
              mountPath: /agdb/pepper
      volumes:
        - name: config
          configMap:
            name: agdb-config
            defaultMode: 511
        - name: pepper
          secret:
            secretName: agdb-pepper
  volumeClaimTemplates:
    - metadata:
        name: agdb-data
        labels:
          app: agdb
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 1Gi

Test that the server is up with curl

The following command must be run from within the cluster unless the server was exposed via LoadBalancer or Ingress. The .default. bit is the name of the namespace where everything was deployed.

curl -v http://agdb.default.svc.cluster.local:3000/api/v1/status # should return 200 OK

Additional considerations

• You could use the localhost:3000/api/v1/status as a startup/readiness/health probe.
• Standard shutdown procedure via the endpoint will not work as K8s will simply restart the server.
• Consider running the cluster rather than just a single node.
• You should be able to adapt the above to other platforms such as AWS EKS.