Managing Docker Containers

Quick Review of Container Image Creation and Usage #

1: Build Image: docker build -t my-app:0.1 .
2: Push to Container Registry: docker push my-app:0.1
3: Pull from Container Registry: docker pull my-app:0.1 [OPTIONAL]
4: Run a Container: docker run my-app:0.1
NOTE: If image does not exist on the host, daemon would pull the image first and then run it
NOTE: A set of images are cached on the host. Daemon would check the cache before pull the image again.

Explain important container management commands #

Pulling an Image:

Download an public image from a Container registry

docker pull <IMAGE_NAME>

Pulling an Image with specific version:

Download a specific version of a public image from a Container registry

# Version or Tag
docker pull <IMAGE_NAME>:<SPECIFIC_VERSION>

# Example:
docker pull node:24.01

Pulling an Private Image from Registry:

To pull a private Docker image from a registry, you need to follow these steps:
- Docker Login: Authenticate with the registry using the docker login command (Default Registry: Docker Hub)
```
# <registry-name>.azurecr.io
docker login <registry-url>
```
- Pull the Image: Use the docker pull command with the full image name (including the registry URL)
```
docker pull <registry-url>/<image-name>:<tag>
```
- Example:
```
  docker login myreg.example.com
  docker pull myreg.example.com/my-private-image:latest
```

Running an Image:

Runs a container in detached mode (container runs in the background) and maps a host port to a container port

# HOST_PORT: The port number on your host machine 
#             where you want to receive traffic
# CONTAINER_PORT: The port number within the container 
#             that's listening for connections
docker run -d -p <HOST_PORT>:<CONTAINER_PORT> <IMAGE_NAME>

Runs a container interactively (you can execute commands) with a terminal session

docker run -it <IMAGE_NAME> /bin/bash

Listing:

List Currently Running Containers

docker container ls

CONTAINER ID   IMAGE          STATUS         NAMES
d1f4e5c8a123   nginx:latest   Up 5 minutes   sharp_haibt
f3c9e7a4b456   redis:alpine   Up 2 hours     eloquent_mo
abc1234def56   mysql:8.0      Up 24 hours    brave_banac

List All Containers (Running + Stopped)

docker container ls -a

CONTAINER ID   IMAGE          STATUS                 NAMES
d1f4e5c8a123   nginx:latest   Up 5 minutes           sharp_haibt
f3c9e7a4b456   redis:alpine   Exited 10 minutes ago  eloquent_mo
abc1234def56   mysql:8.0      Up 24 hours            brave_banac
c4d7e2f9e789   alpine         Exited 2 hours ago     clever_poin

Legacy Equivalent Commands (Still Commonly Used)

docker ps
docker ps -a

Start:

Starts a stopped container

docker container start <CONTAINER_ID or NAME>

Stop:

Stops a running container by sending a SIGTERM signal, followed by a SIGKILL signal after a grace period, terminating all processes in the container
- A SIGTERM signal is a request for a process to terminate gracefully
- While a SIGKILL signal is a forceful and immediate termination

docker container stop <CONTAINER_ID or NAME>

Kill:

Immediately stops a container by sending a SIGKILL signal

docker container kill <CONTAINER_ID or NAME>

Restart:

Restarts a running container

docker container restart <CONTAINER_ID or NAME>

Pause:

Pauses all processes within the container, freezing them in their current state

docker container pause <CONTAINER_ID or NAME>

Unpause:

Unpauses all processes, allowing the container to continue from where it was paused

docker container unpause <CONTAINER_ID or NAME>

Copy Files from Host to Running Container:

Copies a file or directory from your host machine into a running container

docker cp /path/on/host <CONTAINER_ID_or_NAME>:/path/in/container

# Example:
docker cp ./app/config.json my_container:/usr/src/app/config.json

Remove:

Removes one or more stopped containers

docker container rm <CONTAINER_ID or NAME>

Removes all stopped containers

docker container prune

View logs

Fetches the logs of a container

docker logs <CONTAINER_ID or NAME>

2045-06-30T12:00:00Z Starting Nginx server...
2045-06-30T12:00:01Z Listening on port 80
2045-06-30T12:02:15Z GET /index.html 200 OK
2045-06-30T12:03:44Z GET /favicon.ico 404 Not Found
2045-06-30T12:05:10Z Received SIGTERM, shutting down...

Fetches the logs of a container and follows the log output

docker logs -f <CONTAINER_ID or NAME>

Managing Images:

Lists all images on the local machine

docker images

REPOSITORY     TAG       IMAGE ID       CREATED         SIZE
nginx          latest    a1b2c3d4e5f6   2 days ago      142MB
redis          alpine    f6e5d4c3b2a1   1 week ago      32MB
mysql          8.0       1234abcd5678   3 weeks ago     495MB

Displays the history of an image, showing each layer that was created during the build process

docker history <IMAGE_ID>

##simplified
IMAGE          CREATED        CREATED BY       SIZE      COMMENT
a1b2c3d4e5f6   2 days ago     CMD ["nginx"..    0B        -
7f8e9a0b1c2d   2 days ago     EXPOSE 80         0B        -
3c4d5e6f7g8h   2 days ago     RUN apt-get ..   53MB       -
1a2b3c4d5e6f   2 days ago     ADD files ..     22MB       -

Remove:

Delete one or more Docker images from the local system

docker rmi <IMAGE_ID or NAME>

Cleanup:

Removes unused data such as containers, images, networks, and build cache

docker system prune

How do you set memory & CPU usage for containers & get Memory, and CPU usage info about specific containers? #

To limit the memory usage:
- use the --memory (or -m) flag
To limit the CPU usage:
- use the --cpus flag

docker run -d --memory="512m" --cpus="0.5" nginx:latest

# cpus - This restricts the container to use 
#        at most 50% of a single CPU core.
# It doesn't mean the container gets a dedicated half-core
# It means the container will not exceed 0.5 CPU 
# in terms of total CPU time across available cores.

Get Usage for a Specific Container:

docker stats CONTAINER_ID_or_NAME

##simplified
CONTAINER ID   NAME            CPU %     MEM USAGE / LIMIT
d1f4e5c8a123   sharp_haibt     0.45%     25.3MiB / 512MiB

Explain the Docker Container Lifecycle #

Create:

Define a container from an image without starting it

 docker create --name mycontainer myimage

Start:

Run a container that has been created or restart a stopped container

 docker start mycontainer

Run:

Create and start a container in one step

 docker run --name mycontainer myimage

Stop:

Gracefully halt the processes in a running container

 docker stop mycontainer

Kill:

Forcibly stop a running container immediately

 docker kill mycontainer

Pause:

Suspend all processes in a running container

 docker pause mycontainer

Unpause:

Resume all processes in a paused container

 docker unpause mycontainer

Restart:

Stop and then start a container again

 docker restart mycontainer

Remove:

Delete a stopped container from the Docker host

 docker rm mycontainer

How do you get all the system-level information about docker? Like events, disk space, caching, etc.. #

Display system-wide information about Docker installation, including number of containers, images, and storage driver details

docker info

Server Version:           34.0.2
Storage Driver:           overlay2
Number of Containers:     5 (3 running, 2 stopped)
Number of Images:         12
Default Runtime:          runc

Show Docker disk usage, including total and used space for images, containers, and volumes

docker system df

TYPE            TOTAL     ACTIVE SIZE   RECLAIMABLE
Images          12        4      2.4GB  1.5GB (62%)
Containers      5         2      450MB  300MB (67%)
Local Volumes   3         2      600MB  150MB (25%)
Build Cache     15        -      1.2GB  900MB (75%)

Monitor Docker events in real-time, such as container starts/stops, image pulls, and network changes

docker events

2045-06-30T12:34:56Z container create 
  d1f4e5c8a123 (image=nginx:latest, name=sharp_haibt)

2045-06-30T12:34:57Z container start  
  d1f4e5c8a123 (image=nginx:latest, name=sharp_haibt)

2045-06-30T12:36:20Z image pull    
  sha256:def456 (nginx:latest)

2045-06-30T12:38:42Z network connect
  container=abc123 network=bridge

Display real-time CPU, memory, and network usage statistics for running containers

docker stats [container_id]

##simplified
CONTAINER ID   NAME            CPU %     MEM USAGE / LIMIT
d1f4e5c8a123   sharp_haibt     0.45%     25.3MiB / 512MiB

Show the history of an image, including commands and metadata used to create each layer

docker history [image_name]

##simplified
IMAGE          CREATED        CREATED BY       SIZE
a1b2c3d4e5f6   2 days ago     CMD ["nginx"..    0B
7f8e9a0b1c2d   2 days ago     EXPOSE 80         0B
3c4d5e6f7g8h   2 days ago     RUN apt-get ..   53MB
1a2b3c4d5e6f   2 days ago     ADD files ..     22MB

Return low-level information about Docker objects, such as containers, images, networks, and volumes

docker inspect [object_name]

[
  {
    "Id": "abc1234def5678gh9012ijkl3456mnop7890qrstuvwx",
    "Name": "/web_server",
    "Image": "nginx:latest",
    "State": {
      "Status": "running",
      "Running": true,
      "StartedAt": "2045-06-30T12:34:56.789012345Z"
    },
    "NetworkSettings": {
      "IPAddress": "172.17.0.2",
      "Ports": {
        "80/tcp": [
          {
            "HostIp": "0.0.0.0",
            "HostPort": "8080"
          }
        ]
      }
    },
    "Mounts": [
      {
        "Type": "volume",
        "Name": "myvolume",
        "Destination": "/usr/share/nginx/html"
      }
    ]
  }
]

Remove unused data, such as stopped containers, dangling images, and unused networks and volumes
```
docker system prune
```
Remove unused images
```
docker image prune
```
Remove unused containers
```
docker container prune
```
Remove unused networks
```
docker network prune
```

On this page

Quick Review of Container Image Creation and Usage #

Explain important container management commands #

How do you set memory & CPU usage for containers & get Memory, and CPU usage info about specific containers? #

Explain the Docker Container Lifecycle #

How do you get all the system-level information about docker? Like events, disk space, caching, etc.. #