Kubernetes
Kubernetes is an open source container cluster manager that is available as a stand-alone platform or embedded in several distributed platforms including Google’s Container Engine, AWS Elastic Kubernetes Service, Azure Kubernetes Service, and Red Hat OpenShift. Chef Habitat and Kubernetes are complementary. While Kubernetes provides a platform for deployment, scaling, and operations of application containers across clusters of hosts, Chef Habitat manages the build pipeline and lifecycle of those application containers.
Chef Habitat on Kubernetes
Chef Habitat can export your package as a Docker container that runs on Kubernetes in the form of a pod. Additionally, a Chef Habitat bastion pod provides essential gossip ring features like service discovery (binds), secrets and the required initial peer to all other pods.
Chef Habitat robustly deploys the bastion pod with a Kubernetes stateful set, persistent volume, and liveness checking, which ensures node availability and ring data persistence. The Kubernetes stateful set comes with an attached Kubernetes service that makes discoverable with DNS. Each namespace should contain a single service and stateful set.
Deploy the Chef Habitat Bastion on Kubernetes
Complete examples may be downloaded from this folder
To explain how this works, let’s break down the hab-bastion.yaml file:
apiVersion: v1
kind: Service
metadata:
name: hab-bastion
spec:
ports:
- name: gossip-listener
protocol: UDP
port: 9638
targetPort: 9638
- name: http-gateway
protocol: TCP
port: 9631
targetPort: 9631
selector:
app: hab-bastion
clusterIP: None
This service definition creates a virtual IP (VIP), opening access to the Chef Habitat service that runs on the pod.
- The habitat gossip port (9638/UDP) listener
- The habitat http-gateway (9631/TCP) listener
- makes service name available in DNS (as
hab-bastionorhab-bastion.namespace-name, etc) and discoverable by any pod
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: hab-bastion
spec:
spec:
securityContext:
fsGroup: 42
This section sets the group ownership for the persistent volume mount point so the Habitat Supervisor can write to it. The Habitat user (hab) by default has the uid 42 and the gid 42.
containers:
- name: hab-bastion
image: mydockerorigin/hab_bastion:latest
args:
- '--permanent-peer'
The image: line defines the source of the docker container. In this case, the instructions create an image from a Chef Habitat plan using the hab pkg export docker command. It only runs the Chef Habitat Supervisor (hab-sup) service.
The argument --permanent-peer instructs the Supervisor to act as a permanent peer.
resources:
requests:
memory: "100Mi"
cpu: "100m" # equivalent to 0.1 of a CPU core
Resource requests are important because they give instructions to the Kubernetes scheduler–without them, you might overload some nodes while under-using others.
ports:
- name: gossip-listener
protocol: UDP
containerPort: 9638
- name: http-gateway
protocol: TCP
containerPort: 9631
readinessProbe:
httpGet:
path: /
port: 9631
initialDelaySeconds: 5
periodSeconds: 10
livenessProbe:
httpGet:
path: /
port: 9631
initialDelaySeconds: 15
periodSeconds: 20
The livenessProbe tells Kubernetes if the pod is healthy or not. If not, the pod gets restarted.
The readinessProbe signals to Kubernetes that the pod has started up successfully.
volumeMounts:
- name: hab-bastion
mountPath: /hab/sup
volumeClaimTemplates:
- metadata:
name: hab-bastion
spec:
accessModes: [ "ReadWriteOnce" ]
# uncomment if you don't have a default StorageClass
# storageClassName: "standard"
resources:
requests:
storage: 10Gi
All of the Habitat Supervisor’s state data is stored under /hab/sup - we mount this on a persistent volume so it gets re-attached if the pod is ever rescheduled. The data persists!
Create a Kubernetes Deployment That Works with the Bastion
The following is an example of a Kubernetes Stateful Set built from the CockroachDB plan. The Bastion pattern uses the --peer hab-bastion configuration arguments to instruct the Kubernetes pods to use the hab-bastion service as a DNS-resolvable host name.
+++
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: cockroachdb
spec:
selector:
matchLabels:
app: cockroachdb
serviceName: cockroachdb
replicas: 3
template:
metadata:
labels:
app: cockroachdb
spec:
terminationGracePeriodSeconds: 10
securityContext:
fsGroup: 42
containers:
- name: cockroachdb
image: irvingpop/cockroach:latest
args:
- --peer
- hab-bastion
- --topology
- leader
resources:
requests:
memory: "300Mi"
cpu: "500m"
ports:
- name: http
containerPort: 8080
- name: cockroachdb
containerPort: 26257
volumeMounts:
- name: cockroachdb-data
mountPath: /hab/svc/cockroach/data
volumeClaimTemplates:
- metadata:
name: cockroachdb-data
spec:
accessModes: [ "ReadWriteOnce" ]
resources:
requests:
storage: 10Gi
Bare Kubernetes
If your packages don’t require communication with the Chef Habitat Supervisor ring, such as binds, secrets, etc., then you can execute your packages directly on the cluster. You can deploy Chef Habitat packages exported as containers to Kubernetes with the kubectl command. Using the Docker exporter to create a containerized application, you can launch the container like this example:
$ kubectl run mytutorial --image=myorigin/mytutorial --port=8080
Assuming you’re using the Docker image pulled from myorigin/mytutorial, port 8080 on the container should be accessible. Pass networking ports exposed by Chef Habitat with kubectl run as --port options. In this example, the kubectl get command is:
$ kubectl get pods -l run=mytutorial
Docker and ACI
Chef Habitat packages can be exported in both Docker and ACI formats (as well as others). Kubernetes currently supports the Docker runtime and integration of the rkt container runtime (an implementation of the App Container spec) is under active development.
Environment Variables and Networking
Kubernetes supports passing environment variables into containers.
Related Reading
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