Docker Setup

Quickstart: install and run the Docker image

Begin by installing Docker for your OS. Then, to get the SynapseML image and run it, open a terminal (PowerShell/cmd on Windows) and run

docker run -it -p 8888:8888 mcr.microsoft.com/mmlspark/release

In your browser, go to http://localhost:8888/ —you'll see the Docker image EULA, and once you accept it, the Jupyter notebook interface will start. To skip this step, add -e ACCEPT_EULA=yes to the Docker command:

docker run -it -p 8888:8888 -e ACCEPT_EULA=y mcr.microsoft.com/mmlspark/release

You can now select one of the sample notebooks and run it, or create your own.

Note: The EULA is needed only for running the SynapseML Docker image; the source code is released under the MIT license (see the LICENSE file).

Running a specific version

In the preceding docker command, mcr.microsoft.com/mmlspark/release specifies the project and image name that you want to run. There's another component implicit here: the tsag (= version) that you want to use. Specifying it explicitly looks like mcr.microsoft.com/mmlspark/release:1.0.4 for the 1.0.4 tag.

Leaving mcr.microsoft.com/mmlspark/release by itself has an implicit latest tag, so it's equivalent to mcr.microsoft.com/mmlspark/release:latest. The latest tag is identical to the most recent stable SynapseML version. You can see the current [synapsemltags] on our Docker Hub repository.

A more practical example

The previous section had a rather simplistic command. A more complete command that you'll probably want to use can look as follows:

docker run -it --rm \
           -p 127.0.0.1:80:8888 \
           -v ~/myfiles:/notebooks/myfiles \
           mcr.microsoft.com/mmlspark/release:1.0.4

In this example, backslashes are for readability; you can enter the command as one long line if you like. In PowerShell, the myfiles local path and line breaks looks a little different:

docker run -it --rm `
           -p 127.0.0.1:80:8888 `
           -v C:\myfiles:/notebooks/myfiles `
           mcr.microsoft.com/mmlspark/release:1.0.4

Let's break this command and go over the meaning of each part:

• -it

  This command uses a combination of -i and -t (which could also be specified as --interactive --tty). Combining these two flags means that the image is running interactively, which in this example means that you can see messages that the server emits, and it also makes it possible to use Ctrl+C to shut down the Jupyter notebook server.

• --rm

  When Docker runs any image, it creates a container to hold any further filesystem data for files that were created or modified. If you ran the above quickstart command, you can see the container that is left behind with docker container list -a. You can reclaim such containers with `docker container rm

  `, or reclaim all containers from stopped run with `docker container prune`, or even more generally, reclaim all unused Docker resources with `docker system prune`.

  Back to --rm: this flag tells Docker to discard the image when the image exits, which means that any data created while running the image is discarded when the run is done. But see the description of the -v flag.

• -e ACCEPT_EULA=y

  The -e flag is used to set environment variables in the running container. In this case, we use it to bypass the EULA check. More flags can be added for other variables, for example, you can add a -e MMLSPARK_JUPYTER_PORT=80 to change the port that the Jupyter server listens to.

• -p 127.0.0.1:80:8888

  The Jupyter server in the SynapseML image listens to port 8888, but that is normally isolated from the actual network. Previously, we have used -p 8888:8888 to say that we want to map port 8888 (LHS) on our actual machine to port 8888 (RHS) in the container. One problem with this is that 8888 might be hard to remember, but a more serious problem is that your machine now serves the Jupyter interface to any one on your network.

  This more complete example resolves these issues: we replaced 8888:8888 with 80:8888 so HTTP port 80 goes to the container's running Jupyter (making just http://localhost/ work); and we also added a 127.0.0.1: prefix to make the Jupyter inteface available only from your own machine rather than the whole network.

  You can repeat this flag to forward additional ports similarly. For example, you can expose some of the Spark ports, for example: -p 127.0.0.1:4040:4040.

• -v ~/myfiles:/notebooks/myfiles

  As described earlier, we're using --rm to remove the container when the run exits, which is usually fine since pulling out files from these containers can be a little complicated. Instead, we use the -v flag to map a directory from your machine (the ~/myfiles on the LHS) to a directory that is available inside the running container. Any modifications to this directory that are done by the Docker image are performed directly on the actual directory.

  The local directory follows the local filename conventions, so on Windows you'd use a Windows-looking path. On Windows, you also need to share the drive you want to use in the Docker settings.

  The path on the right side is used inside the container and it's therefore a Linux path. The SynapseML image runs Jupyter in the /notebooks directory, so it's a good place for making your files available conveniently.

  This flag can be used more than once, to make several directories available in the running container. Both paths must be absolute, so if you want to specify a path relatively, you can use something like -v $PWD/myfiles:/notebooks/myfiles.

  With such directory sharing in place, you can create/edit notebooks, and code in notebooks can use the shared directory for additional data, for example:

  data = spark.read.csv('myfiles/mydata.csv')
  ...
  model.write().overwrite().save('myfiles/myTrainedModel.mml')

• mcr.microsoft.com/mmlspark/release:1.0.4

  Finally, this argument specifies an explicit version tag for the image that we want to run.

Running the container as a server

An alternative to running the Docker image interactively with -it is running it in a "detached" mode, as a server, using the -d (or --detach) flag. A second flag that may be useful here is --name, which gives a convenient label to the running image:

docker run -d --name my-synapseml ...flags... mcr.microsoft.com/mmlspark/release

When running in this mode, you can use

• docker stop my-synapseml: to stop the image

• docker start my-synapseml: to start it again

• docker logs my-synapseml: to see the log output it produced

Running other commands in an active container

Another useful docker command is exec, which runs a command in the context of an existing active container. To use it, you specify the container name and the command to run. For example, with an already running detached container named my-synapseml, you can use

docker exec -it my-synapseml bash

to start a shell in the context of the server, roughly equivalent to starting a terminal in the Jupyter interface.

Other common Linux executables can be used, for example:

docker exec -it my-synapseml top
docker exec my-synapseml ps auxw

(ps doesn't need -it since it's not an interactive command.)

These commands can be used with interactive containers too, and --name can be used to make them easy to target. If you don't use --name, Docker assigns a random name to the container; you can use docker ps to see it. You can also get the container IDs to use instead of names.

Remember that the command given to docker exec is running in the context of the running container: you can only run executables that exist in the container, and the run is subject to the same resource restrictions (FS/network access, etc.) as the container. The SynapseML image is based on a rather basic Ubuntu installation (the ubuntu image from Docker Hub).

Running other Spark executables

docker run can accept another optional argument after the image name, specifying an alternative executable to run instead of the default launcher that fires up the Jupyter notebook server. Using this extra argument you can use the Spark environment directly in the container:

docker run -it ...flags... mcr.microsoft.com/mmlspark/release bash

This command starts the container with bash instead of Jupyter. This environment has all of the Spark executables available in its $PATH. You still need to specify the command-line flags that load the SynapseML package, but there are convenient environment variables that hold the required package and repositories to use:

pyspark --repositories "$MML_M2REPOS" --packages "$MML_PACKAGE" --master "local[*]"

Many of the above listed flags are useful in this case too, such as mapping work directories with -v.

Updating the SynapseML image

New releases of SynapseML are published from time to time, and they include a new Docker image. As an image consumer, you'll normally not notice such new versions: docker run will download an image if a copy of it doesn't exist locally, but if it does, then docker run will blindly run it, without checking for new tags that were pushed.

Hence you need to explicitly tell Docker to check for a new version and pull it if one exists. You do so with the pull command:

docker pull mcr.microsoft.com/mmlspark/release

Since we didn't specify an explicit tag here, docker adds the implied :latest tag, and checks the available mcr.microsoft.com/mmlspark/release image with this tag on Docker Hub. When it finds a different image with this tag, it will fetch a copy to your machine, changing the image that an unqualified mcr.microsoft.com/mmlspark/release refers to.

Docker normally knows only about the tags that it fetched, so if you've always used mcr.microsoft.com/mmlspark/release to refer to the image without an explicit version tag, then you wouldn't have the version-tagged image too. Once the tag is updated, the previous version will still be in your system, only without any tag. Using docker images to list the images in your system will now show you two images for mcr.microsoft.com/mmlspark/release, one with a tag of latest and one with no tag, shown as <none>. Assuming that you don't have active containers (including detached ones), docker system prune will remove this untagged image, reclaiming the used space.

If you've used an explicit version tag, then it will still exist after a new pull, which means that you can continue using this version. If you used an unqualified name first and then a version-tagged one, Docker will fetch both tags. Only the second fetch is fast since it points to content that was already loaded. In this case, doing a pull when there's a new version will fetch the new latest tag and change its meaning to the newer version, but the older version will still be available under its own version tag.

Finally, if there are such version-tagged older versions that you want to get rid of, you can use docker images to check the list of installed images and their tags, and docker rmi <name>:<tag> to remove the unwanted ones.

A note about security

Executing code in a Docker container can be unsafe if the running user is root. For this reason, the SynapseML image uses a proper username instead. If you still want to run as root (for instance, if you want to apt install an another ubuntu package), then you should use --user root. This mode can be useful when combined with docker exec to perform administrative work while the image continues to run as usual.

Further reading

This text briefly covers some of the useful things that you can do with the SynapseML Docker image (and other images in general). You can find much more documentation online.