with the help of kubernetes I am running daily jobs on GKE, On a daily basis based on cron configured in kubernetes a new container spins up and try to insert some data into BigQuery.

The setup that we have is we have 2 different projects in GCP in one project we maintain the data in BigQuery in other project we have all the GKE running so when GKE has to interact with different project resource my guess is I have to set an environment variable with name GOOGLE_APPLICATION_CREDENTIALS which points to a service account json file, but since every day kubernetes is spinning up a new container I am not sure how and where I should set this variable.

Thanks in Advance!

NOTE: this file is parsed as a golang template by the drone-gke plugin.

---
apiVersion: v1
kind: Secret
metadata:
  name: my-data-service-account-credentials
type: Opaque
data:
  sa_json: "bas64JsonServiceAccount"
---
apiVersion: v1
kind: Pod
metadata:
  name: adtech-ads-apidata-el-adunit-pod
spec:
  containers:
  - name: adtech-ads-apidata-el-adunit-container
    volumeMounts:
    - name: service-account-credentials-volume
     mountPath: "/etc/gcp"
     readOnly: true
  volumes:
  - name: service-account-credentials-volume
    secret:
      secretName: my-data-service-account-credentials
      items:
      - key: sa_json
        path: sa_credentials.json

This is our cron jobs for loading the AdUnit Data

apiVersion: batch/v2alpha1
kind: CronJob
metadata:
  name: adtech-ads-apidata-el-adunit
spec:
  schedule: "*/5 * * * *"
  suspend: false
  concurrencyPolicy: Replace
  successfulJobsHistoryLimit: 10
  failedJobsHistoryLimit: 10
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: adtech-ads-apidata-el-adunit-container
            image: {{.image}}
            args:
            - -cp
            - opt/nyt/DFPDataIngestion-1.0-jar-with-dependencies.jar
            - com.nyt.cron.AdUnitJob
            env:
              - name: ENV_APP_NAME
                value: "{{.env_app_name}}"
              - name: ENV_APP_CONTEXT_NAME
                value: "{{.env_app_context_name}}"
              - name: ENV_GOOGLE_PROJECTID
                value: "{{.env_google_projectId}}"
              - name: ENV_GOOGLE_DATASETID
                value: "{{.env_google_datasetId}}"
              - name: ENV_REPORTING_DATASETID
                value: "{{.env_reporting_datasetId}}"
              - name: ENV_ADBRIDGE_DATASETID
                value: "{{.env_adbridge_datasetId}}"
              - name: ENV_SALESFORCE_DATASETID
                value: "{{.env_salesforce_datasetId}}"
              - name: ENV_CLOUD_PLATFORM_URL
                value: "{{.env_cloud_platform_url}}"
              - name: ENV_SMTP_HOST
                value: "{{.env_smtp_host}}"
              - name: ENV_TO_EMAIL
                value: "{{.env_to_email}}"
              - name: ENV_FROM_EMAIL
                value: "{{.env_from_email}}"
              - name: ENV_AWS_USERNAME
                value: "{{.env_aws_username}}"
              - name: ENV_CLIENT_ID
                value: "{{.env_client_id}}"
              - name: ENV_REFRESH_TOKEN
                value: "{{.env_refresh_token}}"
              - name: ENV_NETWORK_CODE
                value: "{{.env_network_code}}"
              - name: ENV_APPLICATION_NAME
                value: "{{.env_application_name}}"
              - name: ENV_SALESFORCE_USERNAME
                value: "{{.env_salesforce_username}}"
              - name: ENV_SALESFORCE_URL
                value: "{{.env_salesforce_url}}"
              - name: GOOGLE_APPLICATION_CREDENTIALS
                value: "/etc/gcp/sa_credentials.json"
              - name: ENV_CLOUD_SQL_URL
                valueFrom:
                  secretKeyRef:
                    name: secrets
                    key: cloud_sql_url
              - name: ENV_AWS_PASSWORD
                valueFrom:
                  secretKeyRef:
                    name: secrets
                    key: aws_password
              - name: ENV_CLIENT_SECRET
                valueFrom:
                  secretKeyRef:
                    name: secrets
                    key: dfp_client_secret
              - name: ENV_SALESFORCE_PASSWORD
                valueFrom:
                  secretKeyRef:
                    name: secrets
                    key: salesforce_password


          restartPolicy: OnFailure

So, if your GKE project is project my-gke, and the project containing the services/things your GKE containers need access to is project my-data, one approach is to:

Create a service account in the my-data project. Give it whatever GCP roles/permissions are needed (ex. roles/bigquery. dataViewer if you have some BigQuery tables that your my-gke GKE containers need to read).
- Create a service account key for that service account. When you do this in the console following https://cloud.google.com/iam/docs/creating-managing-service-account-keys, you should automatically download a .json file containing the SA credentials.

Create a Kubernetes secret resource for those service account credentials. It might look something like this:

apiVersion: v1
kind: Secret
metadata:
  name: my-data-service-account-credentials
type: Opaque
data:
  sa_json: <contents of running 'base64 the-downloaded-SA-credentials.json'>

Mount the credentials in the container that needs access:

[...]
spec:
  containers:
  - name: my-container
    volumeMounts:
    - name: service-account-credentials-volume
      mountPath: /etc/gcp
      readOnly: true
[...]
  volumes:
  - name: service-account-credentials-volume
    secret:
      secretName: my-data-service-account-credentials
      items:
      - key: sa_json
        path: sa_credentials.json

Set the GOOGLE_APPLICATION_CREDENTIALS environment variable in the container to point to the path of the mounted credentials:

[...]
spec:
  containers:
  - name: my-container
    env:
    - name: GOOGLE_APPLICATION_CREDENTIALS
      value: /etc/gcp/sa_credentials.json

With that, any official GCP clients (ex. the GCP Python client, GCP Java Client, gcloud CLI, etc. should respect the GOOGLE_APPLICATION_CREDENTIALS env var and, when making API requests, automatically use the credentials of the my-data service account that you created and mounted the credentials .json file for.