docker.txt

*Docker*
Basic Docker Commands
    List all available images
    *$ docker images*

    Build an image
    *$ docker build -t [image_name] .*

    Build an image with a version tag
    *$ docker build -t [image_name]:[version] .*

    Tag an image for a registry
    *$ docker tag [image_name]:[version] [registry/image_name:version]*

    Push image to registry
    *$ docker push [registry/image_name:version]*

    Pull an image from registry
    *$ docker pull [registry/image_name:version]*

    Run an image
    *$ docker run [image_name]*

    Run an image with port mapping
    *$ docker run --name [container_name] -p [host_port]:[container_port] [image_name]*

    Run an image in background
    *$ docker run -d --name [container_name] -p [host_port]:[container_port] [image_name]*

    Run an image with environment variables
    *$ docker run -e [KEY]=[VALUE] [image_name]*

    Run an image and get a shell
    *$ docker run --rm -it [image_name] /bin/bash*

    List running containers
    *$ docker ps*

    List all containers
    *$ docker ps -a*

    Run a command within the container
    *$ docker exec -it [container_name/container_id] /bin/bash*

    Stop a container gracefully
    *$ docker stop [container_name]*

    Kill a container immediately
    *$ docker kill [container_name]*

    Start a stopped container
    *$ docker start [container_name]*

    Remove a container
    *$ docker rm [container_name]*

    Remove an image
    *$ docker rmi [image_name]*

    Show logs
    *$ docker logs [container_name]*

    Follow logs live
    *$ docker logs -f [container_name]*

    Inspect full container details
    *$ docker inspect [container_name]*


*Docker Compose*
Most Important Docker Compose Commands
    Start all services
    *$ docker compose up*

    Start all services and rebuild images
    *$ docker compose up --build*

    Start all services in background
    *$ docker compose up -d*

    Show running services
    *$ docker compose ps*

    Show logs
    *$ docker compose logs*

    Follow logs live
    *$ docker compose logs -f*

    Open a shell in a running service
    *$ docker compose exec [service_name] sh*

    Stop services
    *$ docker compose stop*

    Stop and remove the stack
    *$ docker compose down*

    Stop and remove the stack including volumes
    *$ docker compose down -v*

    Validate the compose file
    *$ docker compose config*


*Docker Concepts*
    **Image** Packaged filesystem and startup configuration used to create containers

    **Container** Instance of an image with its own runtime state; can be running or stopped

    **Volume** Persistent storage for container data

    **Network** Way for containers to communicate

    **Registry** Remote place to store and pull images

*Kubernetes*

Mental Model
    **Namespace** Groups resources; not a security boundary by itself.
    **Deployment** Keeps the desired number of Pods running and manages updates.
    **Pod** Runs one or more containers sharing networking and optionally volumes.
    **Service** Stable network endpoint; usually selects Pods by labels, not names.
    **Management** Deployment -> ReplicaSet (maintains replica count) -> Pods -> containers.
    **Traffic** Client -> Service -> ready Pod. The Deployment is not in the traffic path.

Key Fields and Gotchas
    **---** separates resource definitions within a YAML file.
    **replicas** sets the desired Pod count, not the number of Services.
    A Service's **selector** matches Pod **labels** within the same namespace.
    **port** is the Service port; **targetPort** is the destination port number or named container port.
    **spec.template** is the Pod blueprint; changing its image or env triggers a rollout when applied.
    **ClusterIP** exposes the Service inside the cluster. **containerPort** alone publishes nothing.
    **imagePullPolicy: Never** requires the image to already exist on the node; no registry pull.
    **Readiness** controls traffic eligibility; **liveness** restarts unhealthy containers after repeated failures.
    **requests** guide scheduling; **limits** constrain usage (CPU throttling, possible memory OOM kill).
    Delete a Deployment-managed Pod: its ReplicaSet creates a replacement.
    **port-forward** connects to one backing Pod; it does not demonstrate Service load balancing.

Commands
    Commands below use the current context. Check it before mutations; add **--context [context]** to target a specific cluster.
    *$ kubectl config current-context*

    Check cluster
    *$ kubectl cluster-info*

    Apply objects from a YAML manifest
    *$ kubectl apply -f [manifest.yaml]*

    Apply a Kustomize directory (requires a kustomization file)
    *$ kubectl apply -k [k8s_folder]*

    Check common workload resources (get all does not include every resource type)
    *$ kubectl get all -n [namespace]*

    Inspect Pod labels and Service selectors
    *$ kubectl get pods --show-labels -n [namespace]*
    *$ kubectl describe service [service-name] -n [namespace]*

    Wait for rollout
    *$ kubectl rollout status deployment/[app-name] -n [namespace]*

    Expose locally
    *$ kubectl port-forward svc/[service-name] [local_port]:[service_port] -n [namespace]*

    View logs
    *$ kubectl logs deployment/[app-name] -n [namespace]*

    Debug shell
    *$ kubectl exec -it deployment/[app-name] -n [namespace] -- sh*

    Force a new rollout (does not rebuild the image)
    *$ kubectl rollout restart deployment/[app-name] -n [namespace]*

    Scale app
    *$ kubectl scale deployment/[app-name] --replicas=[number] -n [namespace]*

    Delete objects from a YAML manifest; deleting a declared Namespace also deletes everything inside it
    *$ kubectl delete -f [manifest.yaml]*

    Delete a Kustomize app
    *$ kubectl delete -k [k8s_folder]*

References
    Deployments: https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
    Services: https://kubernetes.io/docs/concepts/services-networking/service/
    Probes: https://kubernetes.io/docs/concepts/workloads/pods/probes/
    Resources: https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/