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docker-intro
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Some slides about docker
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Docker Intro =============== This is an Docker introduction slide deck: Slides: <https://smancke.github.io/docker-intro> Source <https://github.com/smancke/docker-intro> Contents: ---------- 1. __Intro__ 1. __Command line interface__ 1. __Build Docker Images__ 1. __Multiple Containers__ 1. __Docker Swarm__ Part 1 ========================= ## Intro What is Docker ================ Key concepts ---------------- * Defined environment for launching processes * Clean separation of environments * Sandbox with defined resources * One simple interface for launching applications What is Docker not! -------------------- * Not a virtualisation * No separate kernel * No hypervisor Installation =============== Docker is linux based, but there exist convenient solutions to work on Windows and Mac OS X also. Detailed Instructions: <https://docs.docker.com/installation/> The simple way for installation in Ubuntu and Debian: curl https://get.docker.com/ | sh docker-machine =================== Simple wrapper over virtualbox (or other backends) to create and manage a Docker host. # create a new machine docker-machine create --driver=virtualbox dev # start an existing machine docker-machine start dev # upgrade the vm image of machine `dev` # must be running docker-machine upgrade dev # list available machines docker-machine ls # activate enviroment variable to machine `dev` eval $(docker-machine env dev) # ssh into machine `dev` docker-machine ssh dev Part 2 ========================= ## Command line interface The Docker hello world ========================= docker run busybox echo 'Hello World' What has happened? * Download the image `busybox` * Create a new container * Execute the `echo` command within the new container Images and Containers ========================== Docker Image --------------- * An immutable template for containers * Can be pulled and pushed towards a registry * Image names have the form `[registry/][user/]name[:tag]` * The default for the tag is `latest` Docker Container --------------- * An instance of an image * Can be started, stopped, restarted, … * Maintains changes within the filesystems * New image can be created from current container state (not recommended, use Dockerfile instead) Commands for image handling ============================== search, pull & push ---------------------- searching in the registry: docker search <term> download or update an image from the registry: docker pull <image> upload an image to the registry: docker push <image> Commands for image handling ============================== list, tag & delete ---------------------- listing of downloaded images: docker images give an image a new name (alias): docker tag <oldname> <newname> delete an image locally: docker rmi <image> Docker run =============== Start a new container docker run <imagename> My favorite run options: Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...] --name Give the container a symbolic name -v, --volume=[] Bind mount a volume -p, --publish=[] Publish a container's port(s) to the host -e, --env=[] Set environment variables --link=[] Add link to another container --restart="no" Restart policy (no, on-failure[:max-retry], always) --rm=false Automatically remove the container when it exits -d, --detach=false Run container in background and print container ID -i, --interactive=false Keep STDIN open even if not attached -t, --tty=false Allocate a pseudo-TTY Some option details ==================== * Publish port 80 from container as port 8080 on host: `-p 8080:80` * Mount local directory `/html` as directory `/usr/share/nginx/html` in the container: `-v /html:/usr/share/nginx/html` * “Mount” just means “make available”. * `/usr/share/nginx/html` is where nginx expects HTML files. Exercise: ---------- 1. Start an nginx web server, accessible on port 8080 on the host, with its default `index.html` file. * Direct your browser to `http://localhost:8080/` to verify that it works. 1. Start an nginx web server, accessible on port 80 on the host, with a custom `index.html` file. * Direct your browser to `http://localhost/` to verify that it works. See your containers: ======================== List containers ----------------- The running containers: docker ps All containers: docker ps -a Show Metadata of a container ----------------------------- docker inspect <container> Output a special field of the metadata: docker inspect --format='{{.Image}}' <container> Container Livecycle ========================= Stop running containers: docker stop <container..> Start stopped containers: docker start <container..> Kill running containers: docker kill <container..> Remove containers: docker rm <container..> Useful tricks: Container Id ============================== give your containers a name docker run --name my_webserver nginx docker rm -f my_webserver save the container id in shell variables c=$(docker run -d nginx) docker rm -f $c start containers in foreground and with `--rm`, when playing around: docker run --rm nginx Interaction and debugging ========================== exec ----- Run a command in an existing container, e.g start a shell docker exec <container> <command> docker exec -it <container> bash logs -------- See the logs (stdout) of the container. docker logs -f <container> copy ------- copy files from and to Docker container, e.g. docker cp my_webserver:/etc/nginx/nginx.conf ~/ Interaction and debugging ========================== Exercise ---------- 1. Start a webserver 2. Overwrite the content of the index.html 3. Watch the webserver logs 4. compare the output of `ps aux` from your container with the host Modify a container =================== Inspect changes on a container's filesystem docker diff <container> Create a new image from a container's changes: docker commit <container> <imagename> Note: ------- - Docker uses layered filesystems, so images and containers only need to store the diff to the their base image Modify a container ========================== Exercise ---------- 1. Search online for the Docker registry image 1. Start a private Docker image registry - Search for the image at <https://hub.docker.com/> - Start the image locally 1. Commit your container’s changes from the previous exercise 1. Push your new image to your private registry 1. Delete the image locally 1. Start the image again (now coming from the registry) Useful tricks: Cleanup Script ======================================= You have to cleanup your local images and old containers regularly. docker rm $(docker ps -q -a -f status=exited) docker rmi $(docker images -q -f dangling=true) Especially on test and build systems this should be part of a cron job. exited=$(docker ps -q -a -f status=exited | wc -l) if [ "$exited" != "0" ]; then docker rm $(docker ps -q -a -f status=exited) fi tagref=$(docker images -q -f dangling=true | wc -l) if [ "$tagref" != "0" ]; then0 docker rmi $(docker images -q -f dangling=true) fi Part 3 ========================= ## Build Docker Images docker build ===================== The normal way to create images is through `Dockerfile` build descriptions. 1. create a `Dockerfile`, e.g. FROM nginx COPY index.html /usr/share/nginx/html/ 2. build the image and give it a name docker build --pull -t my-nginx . Note: --------------------- - The build has the current directory as context - All paths are relative to the Dockerfile - Each command in the Dockerfile creates a new (temporary container) - Every creation step is cached, so repeated builds are fast Dockerfile ===================== FROM -------- The `FROM` instruction sets the Base Image: FROM <image>:<tag> Example: FROM nginx:15:04 Dockerfile ===================== COPY -------- `COPY` can be used to copy files or directories to the image. COPY <src>... <dest> - Source can contain wildcards - If dest does not exist it will be created Example: COPY service.config /etc/service/ COPY service.config /etc/service/myconfig.cfg COPY *.config /etc/service/ COPY cfg/ /etc/service/ Dockerfile ===================== Exercise ---------- Recreate your webserver image with static content using `docker build` Dockerfile ===================== CMD -------- With `CMD` you can specify the default command to execute on container startup. It has two forms. The exec form (preferred): CMD ["executable","param1","param2"] The shell form: CMD executable param1 param2 __Attention__: the shell form starts the command in a sub process, so it will not get the process id 1 and will not receive all signals e.g. from command line or `docker stop`. Example: CMD ["nginx", "-g", "daemon off;"] Dockerfile ===================== ENTRYPOINT ----------- The command in `ENTRYPOINT` will be executed on startup and allows you to configure a container that will run as an executable. - The arguments in `CMD` are passed to the entrypoint by default - If supplied, the `docker run` arguments overwrite those of the `CMD` and are passed as entrypoint arguments. The exec form (preferred): ENTRYPOINT ["executable", "param1", "param2"] Example: ENTRYPOINT ["top", "-b"] CMD ["-c"] Dockerfile ===================== RUN -------- The `RUN` command allows to execute arbitrary commands in the container, which modify the file system and produce a new layered container. RUN <command> It is common to tie related commands together into one RUN command, using shell magic. Example: RUN apt-get update && \ apt-get install -y ca-certificates nginx=${NGINX_VERSION} && \ rm -rf /var/lib/apt/lists/* Dockerfile ===================== ENV ------------------------ `ENV` sets environment variables which are present during container build and remain existent in the image. ENV <key> <value> ENV <key>=<value> ... On container startup they can be overwritten with the `-e` or `--env` option: docker run -e key=value my_image Example: docker run -e message='The answer is' -e answer=42 \ ubuntu \ bash -c 'echo $message $answer' The answer is 42 Dockerfile ========================== Exercise ---------- Create a `greeting` image which can echo a configurable hello world greeting message in ASCII art (e.g. using the ubuntu package figlet): docker run --rm greeting > _ _ _ _ __ __ _ > | | | | __ _| | | ___ | \/ | __ _ _ ____ _(_)_ __ > | |_| |/ _` | | |/ _ \ | |\/| |/ _` | '__\ \ / / | '_ \ > | _ | (_| | | | (_) | | | | | (_| | | \ V /| | | | | > |_| |_|\__,_|_|_|\___/ |_| |_|\__,_|_| \_/ |_|_| |_| docker run --rm -e message=Hi greeting Arthur > _ _ _ _ _ _ > | | | (_) / \ _ __| |_| |__ _ _ _ __ > | |_| | | / _ \ | '__| __| '_ \| | | | '__| > | _ | | / ___ \| | | |_| | | | |_| | | > |_| |_|_| /_/ \_\_| \__|_| |_|\__,_|_| Dockerfile ===================== ADD -------- `ADD` can do the same as `COPY` with the following additions: - If src is an URL, the file is downloaded - If src is a local tar archive, it will be extracted to dest Example: ADD https://download.elasticsearch.org/elasticsearch/elasticsearch/elasticsearch-1.4.4.tar.gz /es/ RUN cd /es && tar xvfz elasticsearch-1.4.4.tar.gz ADD configs.tar.gz /etc/service/ Dockerfile ===================== VOLUME ------------------------ Declare folders for volume mounts. VOLUME ["/data"] Benefit: ------- - The user of your image has explicit documentation of the available mounts - The Docker daemon and cloud tools can persist and backup them - You can use the volumes from other containers by docker run --volumes-from container_with_volumes Dockerfile ===================== EXPOSE ------------------------ With `EXPOSE` an image can declare the ports which should be exported. EXPOSE <port> [<port>...] Benefit: ------- - This information is needed for communication between linked containers - The exposed ports can be used by the `docker run -P`: -P, --publish-all=false Publish all exposed ports to random ports Example nginx ================= FROM debian:jessie MAINTAINER NGINX Docker Maintainers "docker-maint@nginx.com" RUN apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 573BFD6B3D8FBC641079A6ABABF5BD827BD9BF62 RUN echo "deb http://nginx.org/packages/mainline/debian/ jessie nginx" >> /etc/apt/sources.list ENV NGINX_VERSION 1.9.3-1~jessie RUN apt-get update && \ apt-get install -y ca-certificates nginx=${NGINX_VERSION} && \ rm -rf /var/lib/apt/lists/* # forward request and error logs to docker log collector RUN ln -sf /dev/stdout /var/log/nginx/access.log RUN ln -sf /dev/stderr /var/log/nginx/error.log VOLUME ["/var/cache/nginx"] EXPOSE 80 443 CMD ["nginx", "-g", "daemon off;"] Part 4 ========================= ## Multiple Containers Multiple containers ========================== The power of Docker comes in, when you compose your apps out of multiple containers. - Networking - docker-compose Networking Types ========================= By default Docker comes with the following networks: docker network ls NETWORK ID NAME DRIVER 7fca4eb8c647 bridge bridge 9f904ee27bf5 none null cf03ee007fb4 host host Docker can manage networks of different types: * __host__: The host interface * __bridge__: Bridged network interfaces * __overlay__: Software defined multi host network (swarm only) Manage networks with: docker network create|rm|inspect|ls Connect Networks ========================= Containers can be connected to multiple networks. Network at startup: docker run --net=<networkname> <image> Connect a running container: docker network connect <networkname> <containerid> Disconnect a running container: docker network disconnect <networkname> <containerid> docker-compose ================ docker-compose is a simple tool to start multiple containers. Installation: ---------------- curl -L https://github.com/docker/compose/releases/download/1.9.0/docker-compose-`uname -s`-`uname -m` > docker-compose chmod a+x docker-compose Configuration by `docker-compose.yml`: version: '2' services: web: build: . ports: - "5000:5000" volumes: - .:/code redis: image: redis docker-compose usage: ===================== Usage: docker-compose [options] [COMMAND] [ARGS...] docker-compose -h|--help Commands: up Create and start containers down Stop and remove containers, networks, images, and volumes build Build or rebuild services config Validate and view the compose file events Receive real time events from containers exec Execute a command in a running container logs View output from containers ps List containers pull Pull service images push Push service images restart Restart services rm Remove stopped containers scale Set number of containers for a service start Start services stop Stop services .. there are some more .. Exercise =================== 1. Setup a docker-compose project with: - webserver with php - database of choice (e.g. mysql, postgres, or nosql, ...) 2. Implement a counter example in php 3. Scale the webserver compose best practices ============================== * Environment variables can be used * Additional environment variables can be defined in an environment file: `.env` * Image tags can be defined by variables * Compose files can be extended * Use one base file * One extension per environment Part 5 ========================= ## Docker Swarm Docker Swarm ======================= Swarm is a build in Docker clustering mode. It provides: * Single master for communication with the cluster * Monitoring and failover between node * Scaling of containers * Load balancing of published ports Setup a swarm ================ Swarm setup with 3 virtualbox nodes Requirements: * Oracle Virtualbox has to be installed → https://www.virtualbox.org/wiki/Downloads * Docker >= 1.12 * docker-machine → https://docs.docker.com/machine/install-machine/ Swarm - create machines ======================= ## Create three machines with docker-machine for node in node-1 node-2 node-3; do docker-machine create -d virtualbox --virtualbox-memory=1024 $node done docker-machine ls node-1 - virtualbox Running tcp://192.168.99.100:2376 v1.12.6 node-2 - virtualbox Running tcp://192.168.99.101:2376 v1.12.6 node-3 - virtualbox Running tcp://192.168.99.102:2376 v1.12.6 Swarm - create cluster ======================== ## Connect to node-1 and init the swarm master eval $(docker-machine env node-1) docker swarm init --advertise-addr $(docker-machine ip node-1) \ --listen-addr $(docker-machine ip node-1):2377 ## Join the master TOKEN=$(docker swarm join-token -q worker) for node in node-2 node-3; do eval $(docker-machine env $node) docker swarm join --token $TOKEN $(docker-machine ip node-1):2377 done Swarm - create networks ========================= ## create the overlay netwoks eval $(docker-machine env node-1) docker network create --driver overlay --subnet 10.10.1.0/24 logging docker network create --driver overlay --subnet 10.20.1.0/24 web Swarm - create service ======================= ## Create web server eval $(docker-machine env node-1) docker service create --name webserver \ --network logging,web -p 8080:80 nginx docker service create --name redis \ --network logging,web redis Swarm - scale services =========================== ## scale up docker service update --replicas 2 webserver ## scale down docker service update --replicas 1 webserver Further reading =============== [docker.com](https://www.docker.com) [Registry](https://hub.docker.com/) [Commandline reference](https://docs.docker.com/reference/commandline/cli/) [Dockerfile reference](https://docs.docker.com/reference/builder/) [Networking](https://docs.docker.com/engine/userguide/networking/) [docker-compose](https://docs.docker.com/compose/) [Swarm](https://docs.docker.com/engine/swarm/)
