Keystone Federated Swift – False Federation

This is the second post in my series of posts on Swift in a Keystone federated environment, and the first post where I’ll walk through the first environment. The environment I’m calling ‘False Federation’. For details on these series of posts including the rationalisation see my last introductory post.


False Federation

This first environment doesn’t actually use Keystone federation, instead it uses an existing ability of Swift to have more then 1 authentication middleware in the proxy pipeline. Which is why I’m calling this ‘False Federation’.

Swift Reseller’s and the reseller_prefix

Swift, in an OpenStack environment, talks to Keystone for identity management through Keystone’s authtoken and the Swift keystoneauth middlewares. However Keystone isn’t required. Swift was designed to be a complete standalone storage solution, in fact many Swift deployments use different (like swauth) and sometimes custom authentication middlewares. This way people can easily integrate Swift into their own environments.

If you’ve spend anytime setting up authentication middlewares (like keystoneauth) in Swift, you’ve undoubtedly come across Swift’s reseller_prefix option, and maybe thought to yourself why?


As I mentioned earlier from the start Swift was designed to be an end to end standalone storage system. One of the features it has always supported is the idea of more then 1 authentication middleware in the pipeline. And if you have more then 1, then you need a way to distinguish which authentication middleware handles what account. This is what the reseller_prefix does. Swift will match the reseller_prefix prefixed to the account name with the authentication middleware who is to handle it.

This is actually a really powerful feature. It means you could resell your storage solution to other parties to manage accounts, or connect up different parts of your organisation, if say for some reason you have more then 1 source you want to use as an authentication service.

Some authentication middleware’s like Keystoneauth can even cover more then 1 reseller_prefix, this is how service tokens tend to be deployed, so a service can have it’s own namespace of a users for isolation and the data is safe from accidental deletion.

And yes, it’s also possible to set an empty reseller_prefix.


Multiple Keystone middlewares

Having got the idea of reseller_prefixes out of the way, this is the first potential solution and the idea behind ‘False Federation’. If you have a large Swift cluster, you could place the required authentication middlewares for each separate OpenStack environment you want to connect it to.


NOTE: The are 2 middlewares needed to connect to a single Keystone instance, Keystones authtoken and then Swifts keystoneauth. Other authentication middleware, like swauth and many custom ones, are only 1 middleware. So a little less confusing.


Before I get into the configuration I should also mention before you run off and give it a go. The current upstream keystoneauth in Swift doesn’t support being placed multiple times in a pipeline. Why? Because of the way places itself in the wsgi environment. But never fear, I have written a patch to correct this behavior specifically for these set’s of experiments, and when I get a chance to clean it up and write some tests I’ll push it upstream. In the meantime you can grab hold of the patch here.


I’m not going into huge amounts of detail on how to connect to Keystone, the Swift documentation and installation guides to that too well. And really your just duplicating exactly that, but to each Keystone endpoint you want to connect. If you need detailed instructions, then let me know. They say an image is worth more then a 1000 words. So here is a how it’s done in 1 pretty diagram:

The run down is:

  • Edit your proxy-server.conf on each node, and create ‘[filter:authtoken]’ and ‘[filter:keystoneauth]’ sections for each Keystone endpoint. Noting the names of the filters have to be different.
  • Each ‘[filter:authtoken]’ will point to an endpoint, and it’s corresponding ‘[filter:keystoneauth]’ will have a different reseller_prefix which will need to be matched in the Object Storage endpoint on the keystone servers service catalog. (see project documentation)
  • You then place these filters in the proxy pipeline. When placing a pair the authtoken must come before it’s keystoneauth other. But the pair’s ketstoneauth must also appear before then next authtoken (like in the picture).


NOTE: I’ve left of a bunch of middleware options in the picture to keep it small and readable.


Now if I send the following GET requests:
GET /v1/KEY_matt/pictures/cat.png
GET /v1/AUTH_matt/pictures/cat.png


The first would be authenticated on the blue keystone (or via ‘authtoken1 keystoneauth1’) and the second with the green keystone (or via ‘authtoken2 keystoneauth2’).



This approach was to demonstrate what Swift could already do. But there are some limitations to this approach. Which as always depends on your situation. Keystone’s authtoken middelware will always go and try an authenticate. So would add a bunch of latency to each request going through the proxy. If they are close maybe that’s ok. But if this was a geographical cluster with keystones all around the world then… ouch. If using a custom middleware, you’d just skip reseller_prefixes that don’t relate to you (like keystoneauth does).


Maybe you could have a different Swift proxy in each “region” that only points to the local keystone, so you are only authenticating locally.. ok. But then a user can’t come and access their data if they happen to be in a different region.. even though your talking to the same cluster.

So really what we want to do is take advantage of Keystone federation, where we only ever have to talk to 1 instance, the local one for the region a Swift proxy lives. That way we get the speed and the ability to access our data from anywhere.


Next time…

So the next post we’ll add real keystone federation, but assume each federation environment is it’s own cluster, including each has it’s own Swift cluster. In which case we could take advantage of another Swift feature, container sync.

Then the final post would be what we really want, 1 large Swift cluster with multiple Federated keystone OpenStack clusters. But that will involve fiddling with the federation sync metadata and need a more detailed explanation on how Swift authentication works. So first I want to cover what Swift can do simply with the tools it comes with!