15 docker tips in 5 minutes

15 Docker Tips in 5 Minutes Brian Morearty Nov 5, 2013

1. Getting the id of the last-run container

15 Docker Tips in 5 Minutes

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You could do this:

But you have to keep assigning IDs. Try this instead:

!$ ID=$(docker run ubuntu echo hello world)!hello world!$ docker commit $ID helloworld!fd08a884dc79!


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!$ alias dl='docker ps -l -q'!$ docker run ubuntu echo hello world!hello world!$ dl!1904cf045887!$ docker commit `dl` helloworld!fd08a884dc79!


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2. Why you always want a Dockerle, even if you install everything in the shell


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$ docker run -i -t ubuntu bash!root@db0c3978abf8:/# apt-get install postgresql!Reading package lists... Done!Building dependency tree... Done!etc., etc., etc.!root@db0c3978abf8:/# exit!$ docker commit \! -run='{"Cmd":["postgres", "-too -many -opts"]}' \! `dl` postgres!5061b88e4cf0!


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Instead, make a wee liEle Dockerle that is FROM the image you made interacGvely.

There you can set CMD, ENTRYPOINT, VOLUME, etc.


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3. Su-su-sudo


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TOMATO TOMAHTO


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# Add the docker group.!$ sudo groupadd docker!!# Add self to the docker group. !$ sudo gpasswd -a myusername docker!!# Restart the docker daemon!$ sudo service docker restart!!# logout and in again.!$ exit!!


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4. Take out the garbage


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!!$ docker rm $(docker ps -a -q)!

Deletes all stopped containers. (Tries, but conveniently fails, to delete sGll-

running containers.)


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5. jq - the gangsta way to parse docker inspects output !


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!$ docker inspect `dl` | \! grep IPAddress | cut -d '"' -f 4!172.17.0.52!!$ docker inspect `dl` | \! jq -r '.[0].NetworkSettings.IPAddress'!172.17.0.52!!

JSON is for JavaScript. 15 Docker Tips in 5 Minutes

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6. What environment variables does an image have?


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!$ docker run ubuntu env!HOME=/!PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin!container=lxc!HOSTNAME=5e1560b7f757!

This is nice when using docker run -link to connect containers. (Later slide.)


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7. RUN vs. CMD instruction


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!FROM thelanddownunder!MAINTAINER crocdundee!!# docker build will execute these:!RUN apt-get update!RUN apt-get install softwares!!# docker run runs this cmd by default:!CMD ["softwares"]!

A Dockerle. 15 Docker Tips in 5 Minutes

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8. CMD vs. ENTRYPOINT instruction


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!$ cat Dockerfile!FROM ubuntu!CMD ["echo"]!!$ docker run \ imagename \ echo hello!hello!!


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!$ cat Dockerfile!FROM ubuntu!ENTRYPOINT ["echo"]!!$ docker run \ imagename \ echo hello!echo hello!!

Overrideable.

Not overrideable.

9. Does a Docker container have its own IP address?


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!$ ip -4 -o addr show eth0!2: eth0 inet 162.243.139.222/24!!$ docker run ubuntu \! ip -4 -o addr show eth0!149: eth0 inet 172.17.0.43/16!

Yep. Its like a process with an IP address. 15 Docker Tips in 5 Minutes

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10. Dockers architecture: thin CLI client, REST server daemon over UNIX socket


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!# Connect to the UNIX socket and make!# like an HTTP client.!$ nc -U //var/run/docker.sock!GET /images/json HTTP/1.1!!HTTP/1.1 200 OK!Content-Type: application/json!Date: Tue, 05 Nov 2013 23:18:09 GMT!Transfer-Encoding: chunked!!16aa![{"Repository":"postgres","Tag":.........!

Orange is what I typed. 15 Docker Tips in 5 Minutes

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11. Graph the dependencies among your images


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!# Generate an image dependency diagram!$ docker images -viz | \! dot -Tpng -o docker.png!!# To see it, run this on the host:!$ python -m SimpleHTTPServer!!# then browse to:!# http://machinename:8000/docker.png!


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And hope yours doesnt look like this.


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12. Where does Docker store everything?


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!$ sudo su!# cd /var/lib/docker!# ls -F!containers/ graph/ repositories volumes/!

Explore! graph means images. Filesystem layers are in graph/imageid/layer.


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13. Docker source code: Go, Go, Go, Grabote.


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commands.go The CLI.

api.go The REST API router.

server.go ImplementaGon of much of the the REST API.

buildle.go The Dockerle parser.

14. RUN some daemons, exit the container. What happens?


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$ cat Dockerfile!FROM ubuntu:12.04!MAINTAINER Brian Morearty!...!RUN pg_ctl start ...!!$ docker run -i -t postgresimage bash!root@08d363f57161:/# ps aux!# Doesnt show postgres daemon!

Dont run a daemon in your Dockerle. 15 Docker Tips in 5 Minutes

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15. Letting containers talk to each other


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I saved the best for last.

# Run a container. Give it a name.!$ docker run -d -name loldb loldbimage!!# Run another. Link it to the first,!# using an alias.!$ docker run -link /loldb:cheez \! otherimage env!CHEEZ_PORT=tcp://172.17.0.8:6379!CHEEZ_PORT_1337_TCP=tcp://172.17.0.8:6379!CHEEZ_PORT_1337_TCP_ADDR=172.17.0.12!CHEEZ_PORT_1337_TCP_PORT=6379!CHEEZ_PORT_1337_TCP_PROTO=tcp!!

This sets up a bridge. 2nd container needs to know aliased name (CHEEZ) and port (1337).


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Extracted from my intro-level Hands on with Docker class. (In partnership with Docker, Inc.) Beta class this Monday, 6-9pm. handsonwith.com


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15 docker tips in 5 minutes

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