Configuring liveness and readiness probes for Kubernetes Deployment

The 400 error is because the ALLOWED_HOSTS forbids requests using localhost as a hostname. You should include the header Host: lms or Host: cms

You can add the header to the probe:

          livenessProbe:
            httpGet:
              httpHeaders:
                - name: Host
                  value: lms
              path: /heartbeat
              port: 8000

Or you can edit your ALLOWED_HOSTS setting.