I’m doing something of a tour of the in-house PaaS world at the moment. And in my quest I stumbled upon Juju, which at first seemed like a PaaS solution to me. It is not. 🙂 I just found the concept interesting so I’ll do a short write up.
It can resemble a PaaS in many ways, but it is also different in certain areas you would expect from a PaaS. I’ll get back to that.
I have only done some basic testing of Juju, so let me know if something is off. This is just an initial summary of my thoughts.
The Platform
Juju is a tool for automation of provisioning and deployment tasks from Ubuntu. It seems to have been around for a couple of years, and they just recently launched the Juju Charm store. Which is awesome. It is a flexible solution, but also quite low level. You can check out this post for more details around the launch and thoughts about usage .
Main concepts
A Juju Charm is basically what you deploy in Juju. You can find a list of pre-existing charms at (http://jujucharms.com)[http://jujucharms.com] . It is just a package of files where some names have special meaning (comparable to DEB or RPM in some ways) and contain scripts or files that contain meta data. metadata.yaml is the descriptor for the package and Hooks are specially named scripts that will be triggered at different times in the life cycle. The usual ones are start, stop and install. The scripts can be written in most “executable” languages in Linux meaning Bash, Python etc.
All features of Juju are deployed as charms. So wether you would like to provide MySQL to your applications, or deploy your own Java application it is deployed and built as a Charm. By default Juju orchestrates the platform beneath (MaaS or Iaas) so that each Charm is deployed to a separate machine/virtual machine. Now that is only half right; as you can also add an extra unit to a deployed Charm which also becomes another machine. This is the way you scale in Juju.
When you need to use MySQL from an application you tie a relation between them. The same goes for using the HAProxy in front of your application. When you tie a relation you can use hooks on either side to perform operations. So when you add a relation to HAProxy, the proxy is updated with the address of the web application to serve. The same relation-hooks will be triggered if you add another unit to the web application (scale out).
If you deploy MySQL in three units that equals three VMs on Amazon. This makes it a bit slower at scaling out than other solutions where they utilize free resources on (bigger) already existing VMs.
Getting started
It is quite fast to get started on AWS. It is just an easy install via gems, and a bootstrap command. It bootstraps a single node for control and creates an S3 bucket for state. You can find a quick and easy getting started guide here. Nodes are not provisioned before you deploy each charm. This makes it a bit slower in deploying the actual application, but the boot up time (plus whatever you need to install for that application) for a new VM isn’t too bad actually.
The whole deploying a Charm process is a little too quiet, and I can’t find a way to make it more verbose. You can peek into the platform with juju debug-log, but it is still hard to debug failing relationships.
The concepts seem flexible, but basic. Juju doesn’t monitor and keep your Java processes alive like most PaaS solutions would. This goes for both a node that goes dead or a process that dies. I do think Juju could benefit from some more monitoring and recovery even though it’s not meant to be a PaaS.
My thoughts
I find the concept of Juju quite intriguing, and it is very flexible. You can use it as something to deploy your Java application or you can use it to deploy an Openstack IaaS. The relations hooks is a good concept, and the ease of getting started is one of the best I have experienced for this kind of product.
The number of charms available is limited, and the quality varies. I tried some charms, and while they seemed to deploy correctly I could not get stuff really working (some worked). I tested WordPress, MySQL, HAProxy, Gitlab, Openstack and Jenkins. So good concepts, but so far it seems a bit lacking in execution. It really is easy deploying all those services, so if the guiding/installation/implementation worked it would probably rock.
The relation hooks are a quite good way to handle dependencies and relationships but I really would like it to install and configure MySQL as well when it is actually required for WordPress. Right now this is three separate commands. This is probably because they have a concept where the dependency can be satisfied by several products (DBs in this case), but for ease of use it should be possible to specify a default that is set up automatically if nothing else exists.
You can also combine Juju with something like Puppet easily, but it will probably have a much smaller part to play as Juju essentialy focuses on small use-and-throw VMs. There is an addition called Jitsu that lets you deploy multiple Charms on fewer machines. But I actually think that would move Juju into a PaaS area, and one quite lacking in features (guaranteed isolation, dynamic re-allocation and monitoring).
It does not handle processes and dynamic re-allocation which is an important part of what we look for in a platform, so as a general purpose platform for running Java apps I would not choose it. Most PaaS solutions seems like a better option. I’ll get back to some of the PaaS alternatives in-house in another post. To be fair: Juju doesn’t seem to target that kind of deployment either, it’s just not what I am looking for right now.
It is probably a tool I will keep using though. As I am writing this I am spinning up a Puppetmaster and a couple of Puppet slaves on AWS for some testing. It’s quick and easy, and I hope the number of charms increases moving forward. I´ll keep checking back on this one as a tool in my toolbox.
