On May 5th 2017 the Docker engineering team released version v17.05.0-ce of the Docker CE product. The versioning is relatively new and follows a similar pattern to the Ubuntu project - YY.MM - so the next version will be 17.06 for June. CE stands for Community Edition and differentiates between this and the commercial offering. Like most well-managed open-source projects a high-level changelog is provided with each release - this lets us know what new features are available and sometimes these link to Pull Requests to give additional context and discussion. In this post I'll highlight a few of the changes. ### Multi-stage builds The long-awaited multi-stage builds were made available in the 17.05 CE release and also highlighted in the Dockercon keynote. This feature helps you separate your build-time dependencies from your runtime environment. In the case of a small Golang Dockerfile your resulting image could go from around 600MB in size to under 10MB. * [Multi-staged builds tutorial](http://blog.alexellis.io/mutli-stage-docker-builds/) ### --mount flag for `docker run` The syntax for mounting volumes in `docker run` and Swarm is very different and that means learning two sets of syntax. The `--mount` change means `docker run` can now use the syntax from `docker swarm create`. In this example I'll show the various options for mounting using the [Portainer project](http://portainer.io/) which provides a free, feature-rich UI for Docker and Swarm. Mounting a Docker volume with `docker run` ``` $ docker run -v /var/run/docker.sock:/var/run/docker.sock \ -p 9000:9000 -d portainer/portainer -H unix:///var/run/docker.sock ``` In Swarm you would have typed in: ``` docker service create \ --publish 9000:9000 \ --mount type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock \ portainer/portainer -H unix:///var/run/docker.sock ``` You can see the syntax is much more verbose and can be harder to remember. `docker run` can now use this same syntax: ``` docker run \ -p 9000:9000 \ --mount type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock \ -d portainer/portainer -H unix:///var/run/docker.sock ``` ### Dockerfile via stdin A new change to the user experience means that you can now read a Dockerfile over `stdin`. I'm not sure this is a change everyone will need in their toolbox but advanced users may make use of it for scripting. It means that rather than reading a Dockerfile from disk - you can read it from the output of another program or the bash console. Example: ``` $ docker build -t my-image . -f - FROM alpine RUN apk --no-cache add curl CMD ["curl"] (Control + D) ``` Did you know that the `-f` flag allows you to specify a different name or path for your Dockerfile? This can be useful when maintaining projects for different architectures. You could maintain a Dockerfile for Raspberry Pi called `Dockerfile.armhf` for instance and then build it on a RPi with `docker build -t myimage:pi. -f Dockerfile.armhf`. ### Secrets get formatting The CLI has improvements around inspecting and listing secrets created on your swarm. For instance here is the regular output: ``` $ docker secret ls ID NAME CREATED UPDATED 180246v1yjayukr64ioxpgubw func_accesskey 3 weeks ago 3 weeks ago i1u0q0uhc7qxcmj6kr37kvv5a func_secretkey 3 weeks ago 3 weeks ago ``` With a custom format you can pick whatever values you are interested in. The `--format` flag is already available for other commands like `docker network inspect` and `docker inspect` (for containers). This gives us the `id` alone (useful for piping to `xargs` or scripts) ``` docker secret ls --format "{{.ID}}" ``` This gives the Name plus any Labels associated: ``` $ docker secret ls --format "{{.Name}}\t{{.Labels}}" func_accesskey com.docker.stack.namespace=func func_secretkey com.docker.stack.namespace=func ``` ### Setting up the daemon's data root The `--graph` flag that can be configured on the Docker daemon to specify the root folder of your Docker library has had a name change. The flag is now called `--data-root`. If you're using `--graph` or `-G` you don't need to change just yet but if you want to then find your systemd file with `systemctl status docker`. I'm on Ubuntu here so my file is at: `/lib/systemd/system/docker.service`. So we can change the Docker data root from `/var/lib/docker` if we want to anything else by adding `--data-root` to our systemd file: ``` ExecStart=/usr/bin/dockerd -H fd:// --data-root=/mnt/ssd/lib/docker ``` ### Task logs for Docker Swarm You can now fetch the logs for individual tasks or replicas for your Docker Swarm services. An example may be an NGinx webserver: ``` $ docker service create --name web --publish 80:80 --replicas=2 nginx ``` Your services will show up with two replicas or (tasks). ``` $ docker service ls ID NAME MODE REPLICAS IMAGE PORTS sd86rprefd4c web replicated 2/2 nginx:latest *:80->80/tcp ``` You can find the list of task ids from `docker service ps web`. The logs will be empty - so use `curl` to create some log entries, then review the logs. ``` $ curl http://localhost:80/page_a -4 $ curl http://localhost:80/page_b -4 ``` Each replica will get one log entry. ``` $ docker service ps web ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS 1qzlqimfu5fi web.1 nginx:latest alexx Running Running 13 seconds ago 9oq9jz40vwfy web.2 nginx:latest alexx Running Running 13 seconds ago ``` Now checkout the logs of each individual task using the value from the `ID` column: ``` $ docker service logs 1qzlqimfu5fi web.1.1qzlqimfu5fi@alexx | 10.255.0.2 - - [15/Jun/2017:21:07:42 +0000] "GET /page_b HTTP/1.1" 404 169 "-" "curl/7.47.0" "-" $ docker service logs 9oq9jz40vwfy web.2.9oq9jz40vwfy@alexx | 10.255.0.2 - - [15/Jun/2017:21:07:38 +0000] "GET /page_a HTTP/1.1" 404 169 "-" "curl/7.47.0" "-" ``` This will definitely be a handy feature for debugging services - especially when you need targeted logs. #### Wrapping up There's quite a few additional changes around the Docker Swarm CLI which you can read in the [Changelog notes](https://github.com/moby/moby/releases/tag/v17.05.0-ce) over on Github. If you found this useful then checkout my archive of Docker and Swarm tutorials below: * [Raspberry Pi guides & tutorials](http://blog.alexellis.io/tag/raspberry-pi/) * [Docker tutorials](http://blog.alexellis.io/tag/docker/) * [Docker Swarm tutorials](http://blog.alexellis.io/tag/swarm/) > Follow me on Twitter [@alexellisuk](https://twitter.com/alexellisuk) ##### Share on Twitter

Let's take a look at the top 6 changes in Docker's May release 17.05 CE. @Docker https://t.co/tV7W1DHVT8
— Alex Ellis (@alexellisuk) June 19, 2017

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