Demo Docker for Mac

Demonstration of:

• Docker software containerization platform
• Docker Community Edition for Mac

Setup

Get Docker for Mac.

Option 1: Download a .dmg file:

https://docs.docker.com/docker-for-mac/

Option 2: Use brew:

$ brew cask install docker

Verify:

$ docker --version
Docker version 18.03.1-ce, build 9ee9f40

$ docker-compose --version
docker-compose version 1.21.1, build 5a3f1a3

$ docker-machine --version
docker-machine version 0.14.0, build 89b8332

Launch

Launch Docker.app:

• Sign in with your Docker id and password.

• You should see a dialog "Docker is now up and running!"

• You should see a Docker icon in your menu bar.

Run

Run a "hello world" container:

$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
9bb5a5d4561a: Pull complete
Digest: sha256:f5233545e43561214ca4891fd1157e1c3c563316ed8e237750d59bde73361e77
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (amd64)
3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
https://hub.docker.com/

For more examples and ideas, visit:
https://docs.docker.com/engine/userguide/

Troubleshoot "Cannot connect to the Docker daemon"

Symptom:

Cannot connect to the Docker daemon at unix:///var/run/docker.sock.
Is the docker daemon running?

Treatment:

• Docker may have quit or crashed. Try to launch Docker.

• On macOS, you should see the Docker icon in your menubar.

• On macOS, you should see the Docker socket:

  $ ls -la /var/run/docker.sock lrwxr-xr-x 1 root daemon 64 Jul 2 10:31 /var/run/docker.sock -> /Users/me/Library/Containers/com.docker.docker/Data/s60

Troubleshoot "permission denied"

Symptom:

docker: Got permission denied while trying to connect to the 
Docker daemon socket at unix:///var/run/docker.sock: 
Post http://%2Fvar%2Frun%2Fdocker.sock/v1.37/containers/create: 
dial unix /var/run/docker.sock: connect: permission denied.

Treatment:

• The error message tells you that your current user can’t access the docker engine, because you’re lacking permissions to access the unix socket to communicate with the engine.

• Verify the issue affects any Docker command:

  $ docker ps
  

• View the socket:

  $ ls -la /var/run/docker.sock lrwxr-xr-x 1 root daemon 57 Jul 2 10:11 /var/run/docker.sock -> /Users/me/Library/Containers/com.docker.docker/Data/s60

• On macOS, did you launch Docker as one user, then switch to a second user? The treatment is to switch to the first user, then stop all Docker containers, then switch to the second user, then start Docker.

  $ docker stop $(docker ps -aq)
  

• See https://techoverflow.net/2017/03/01/solving-docker-permission-denied-while-trying-to-connect-to-the-docker-daemon-socket/

• As a temporary solution, use sudo to run the failed command as root.

• As a permanent solution, fix the issue by adding the current user to the docker group.

  • On Linux:

    sudo usermod -a -G docker $USER

  • On macOs:

    TODO

• Completely log out of your account and log back in. If in doubt, reboot!

• After doing that, you should be able to run the command without any issues. Run docker run hello-world as a normal user in order to check if it works. Reboot if the issue still persists. Logging out and logging back in is required because the group change will not have an effect unless your session is closed.

Experiment

Experiment with various commands:

$ docker images
$ docker ps
…

Stop the "hello world" container:

$ docker stop hello-world

Run a demo webserver

Run a webserver container, such as the NGINX webserver container:

$ docker run -d -p 80:80 --name webserver nginx
Unable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
…

Browse http://localhost/ to bring up the home page.

• You should see "Welcome to nginx!"

Experiment with various commands:

$ docker images
$ docker ps
…

Stop the container:

$ docker stop webserver

Create a webserver using a Dockerfile

This section thanks to https://www.katacoda.com/courses/docker/create-nginx-static-web-server

Demonstration of:

• A container based on Alpine Linux and Nginx webserver
• How to create a Dockerfile

Create any directory:

$ mkdir demo
$ cd demo

Create a file named Dockerfile with this text:

FROM nginx:alpine
COPY . /usr/share/nginx/html

Build:

$ docker build -t webserver-image:v1 .
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM nginx:alpine
alpine: Pulling from library/nginx
ff3a5c916c92: Pull complete
d81b148fab7c: Pull complete
f9fe12447daf: Pull complete
ad017fd52da2: Pull complete
Digest: sha256:4a85273d1e403fbf676960c0ad41b673c7b034204a48cb32779fbb2c18e3839d
Status: Downloaded newer image for nginx:alpine
---> bc7fdec94612
Step 2/2 : COPY . /usr/share/nginx/html
---> da3fb243e03a
Successfully built da3fb243e03a
Successfully tagged webserver-image:v1

Troubleshoot "unable to prepare context"

Symptom:

unable to prepare context: unable to evaluate symlinks in Dockerfile path: lstat /Users/joel-omniex/tmp/demo-docker-area/Dockerfile: no such file or directory

Treatment:

• The error message shows that Docker is not finding a Dockerfile. Do you have a Dockerfile in the directory, and is it readable?

Run

Run:

$ docker run -d -p 80:80 webserver-image:v1

Get the container's custom name:

$ docker ps
CONTAINER ID        IMAGE                COMMAND                  CREATED             STATUS              PORTS                NAMES
7f5d8f957039        webserver-image:v1   "nginx -g 'daemon of…"   2 minutes ago       Up 2 minutes        0.0.0.0:80->80/tcp   blissful_bhaskara

Stop the container with its custom name

$ docker stop blissful_bhaskara

Troubleshoot: port is already allocated

Symptom:

docker: Error response from daemon: driver failed programming 
external connectivity on endpoint adoring_kapitsa 
(3557175705a1c0c3974d31261528917946b698c9a7f9696a2a0bd82d03b87fa4): 
Bind for 0.0.0.0:80 failed: port is already allocated.

Treatment:

• Option 1: Find out what's using port 80 then stop it e.g. try docker images, try docker stop hello-world, try docker stop webserver.

• Option 2: Use a different port e.g. docker run -d -p 81:81 webserver-image:v1

Add web page

The Dockerfile above automatically copies all the local files to the NGINX html directory, because of this line:

COPY static-html-directory /usr/share/nginx/html

When you run the docker build command above, you see the copy happen:

Step 2/2 : COPY . /usr/share/nginx/html

The Docker container NGINX automatically serves a file name index.html, because of the NGINX default configuration.

Create your own index.html file in the directory:

echo "Demo" > index.html

Restart:

$ docker restart blissful_bhaskara 

Browse http://localhost then reload the page in your browser, and you should see the "Demo" text.

See also

• Rebuild Docker container on file changes