All MongoDB releases, everywhere

One of my “official side projects” is the Go language driver for MongoDB, started a few years back while looking for a way to store data conveniently from the Go language while leaving aside some of the problems we have mapping code into table-based approaches.

Nowadays this is used in projects at Canonical, in the MongoDB tooling itself, and also in some of my own personal projects. For the personal server-side projects I’ve been using docker containers to conveniently deploy the database tooling, but this week when I went to update some of my older images pulled from the docker hub I found that the docker installed on that server was a bit too old, so it was time to update the servers.

But that got me wondering: what if I replaced all those containers by snaps? This would allow me to keep the convenience and safety of the isolation, while making a lot of things simpler. Unlike docker, snaps make the installed tooling more easily accessible to the host system (bins in the search path, processes as actual children from shell and systemd, etc), and can even use system resources directly assuming interfaces allow it (e.g. home files).

So I got into that, and perhaps ended up overdoing it a little bit. Based on my experience testing the driver, I really appreciate having all versions available for playing with, rather than just the latest one. This is how my local development system looks like right now:

$ snap list | grep 'Name\|mongo'
Name                  Version               Rev     Developer   Notes
mongo22               2.2.7                 1       niemeyer    -
mongo24               2.4.14                1       niemeyer    -
mongo26               2.6.12                1       niemeyer    -
mongo30               3.0.12                1       niemeyer    -
mongo32               3.2.7                 1       niemeyer    -
mongo33               3.3.9                 1       niemeyer    -

These are backed by upstream tarballs (snapcraft downloaded them pre-built from mongodb.com), and are all installed, running, and with tooling available for playing with. They are also published to the snap store which means you can easily make use of them locally as well. If you want to do that, here is a crash course on snaps and on how I packaged the database together specifically.

If you’re using Ubuntu, update to release 16.04 which has snaps working out of the box. For other distributions have a look at snapcraft.io to see what command must be run for ensuring it is available.

Then, pick your version and install it. For example, if you want to play with the features just announced at MongoDB World this week, you want the unstable version 3.3.9:

$ snap install mongo33
93.59 MB / 93.59 MB [============================] 100.00 % 1.33 MB/s 

Name     Version  Rev  Developer  Notes
mongo33  3.3.9    1    niemeyer   -

After that you already have the tooling available in your path (assuming you have /snap/bin there), and the daemon started. So go ahead and fire the client to talk to the database:

$ mongo33
MongoDB shell version: 3.3.9
connecting to: 127.0.0.1:3317/test
MongoDB server version: 3.3.9
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
        http://docs.mongodb.org/
Questions? Try the support group
        http://groups.google.com/group/mongodb-user
Server has startup warnings: 
(...) 
(...) ** NOTE: This is a development version (3.3.9) of MongoDB.
(...) **       Not recommended for production.
> 

Note that the server started on the non-standard port 33017 to allow multiple versions to be running together. The pattern is that the snap mongoNN will run on port NN017.

The tools installed also follow a similar pattern. Where upstream uses mongo, mongod, mongodump, etc, the snaps will have them under /snap/bin as mongo33, mongo33.d, mongo33.dump, and so on.

The systemd unit, if you want to interact with it for restarting, improving, debugging, etc, is named snap.mongo33.mongod.service, as usual for any snap that contains a daemon (snap.<snap name>.<app name>.service).

The data for the process that runs under systemd lives in the the standard writable area that the confinement system opens up for snaps in general – in this specific case /var/snap/mongo33/common/. The common directory is reused untouched on updates across snap revisions, which implies snapd won’t copy the data over when doing such updates. This compromises slightly the update safety, but is worth it for bulk data that we don’t want to copy on every snap refresh.

So this ended up quite nicely. Next up is the Go server code itself, which will be packed as a snap too, for deploying it into the servers in a similar way. The exact details for how these snaps are being built are publicly available too.

If you want a hand doing something similar, we have some helpful people at #snappy on FreeNode and also [email protected]

@gniemeyer

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