A stateless application does not retain knowledge of client sessions or past transactions between requests. Each request can therefore be handled without requiring the same server. section 15.4.3
A Kubernetes deployment uses statelessness to:
- Run identical Pods from a container image under a Deployment. section 15.4.3
- Group Pods behind a Service with a stable cluster IP and label-based endpoint discovery. section 15.4.3
- Expose the workload externally by changing the Service to type LoadBalancer. section 15.4.3
Migrated Tomcat workload
A Migrate for Anthos-generated deployment_spec.yaml creates a Tomcat Deployment and Service. Applying it with kubectl starts the Pod; a LoadBalancer Service makes the application externally reachable. section 15.4.3
Listing 15.1 The deployment_spec.yaml generated by M4A
# Stateless application specification
# The Deployment creates a single replicated Pod, indicated by the 'replicas' field
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
app: tomcat-vm-gulli-vm
migrate-for-anthos-optimization: "true"
migrate-for-anthos-version: v1.5.0
name: tomcat-vm-gulli-vm
spec:
replicas: 1
selector:
matchLabels:
app: tomcat-vm-gulli-vm
migrate-for-anthos-optimization: "true"
migrate-for-anthos-version: v1.5.0
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
app: tomcat-vm-gulli-vm
migrate-for-anthos-optimization: "true"
migrate-for-anthos-version: v1.5.0
spec:
containers:
- image: gcr.io/named-tome-295414/tomcat-vm-gulli-vm:11-13-2020--15-0-39
name: tomcat-vm-gulli-vm
readinessProbe:
exec:
command:
- /code/ready.sh
resources: {}
securityContext:
privileged: true
volumeMounts:
- mountPath: /sys/fs/cgroup
name: cgroups
volumes:
- hostPath:
path: /sys/fs/cgroup
type: Directory
name: cgroups
status: {}
---
# Headless Service specification -
# No load-balancing, and a single cluster internal IP, only reachable from within the cluster
# The Kubernetes endpoints controller will modify the DNS configuration to return records (addresses) that point to the Pods, which are labeled with "app": "tomcat-vm-gulli-vm"
apiVersion: v1
kind: Service
metadata:
creationTimestamp: null
name: tomcat-vm-gulli-vm
spec:
clusterIP: None
selector:
app: tomcat-vm-gulli-vm
type: ClusterIP
status:
loadBalancer: {}
---
Inspect the generated YAML showing the stateless Deployment, replica setting, image, selectors, and Pod template. section 15.4.3
