Creating an Ansible Inventory file using Jinja templating

While there are lots of tools in Ansible for generating an inventory file dynamically, in a system like this, you might want to be able to perform additional operations against the same cluster. For example, once the cluster has been running for a few months, you might want to do a Yum update. Eventually, you want to de-provision. Thus, having a remote record of what machines make up a particular cluster can be very useful. Dynamic inventories can be OK, but often it takes time to regenerate the inventory, and that may slow down an already long process, especially during iterated development.

So, I like to generate inventory files. These are fairly simple files, but they are not one of the supported file types in Ansible. Ansible does support ini files, but the inventory files have maybe lines that are not in key=value format.

Instead, I use Jinja formatting to generate inventory files, and they are pretty simple to work with.

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Getting Shade for the Ansible OpenStack modules

When Monty Taylor and company looked to update the Ansible support for OpenStack, they realized that there was a neat little library waiting to emerge: Shade. Pulling the duplicated code into Shade brought along all of the benefits that a good refactoring can accomplish: fewer cut and paste errors, common things work in common ways, and so on. However, this means that the OpenStack modules are now dependent on a remote library being installed on the managed system. And we do not yet package Shade as part of OSP or the Ansible products. If you do want to use the OpenStack modules for Ansible, here is the “closest to supported” way you can do so.

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Using JSON home on a Keystone server

Say you have an AUTH_URL like this:

$ echo $OS_AUTH_URL

And now you want to do something with it.  You might think you can get the info you want from the /v3 url, but it does not tell you much:

$ curl $OS_AUTH_URL 
{"version": {"status": "stable", "updated": "2016-10-06T00:00:00Z", "media-types": [{"base": "application/json", "type": "application/vnd.openstack.identity-v3+json"}], "id": "v3.7", "links": [{"href": "", "rel": "self"}]}}[ayoung@ayoung541 salab]$

Not too helpful.  Turns out, though, that there is data, it is just requires the json-home accepts header.

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Fixing Bug 96869

Bug 968696

The word Admin is used all over the place. To administer was originally something servants did to their masters. In one of the greater inversions of linguistic history, we now use Admin as a way to indicate authority. In OpenStack, the admin role is used for almost all operations that are reserved for someone with a higher level of authority. These actions are not expected to be performed by people with the plebean Member role.

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Why Quotas are Hard

A quota is a numerical limit on a group of resources. Quotas have to be both recorded and enforced.

We had a session at the summit this past week about hierarchical quotas and, if I took anything away from it, it is that quotas are hard.

Keystone supports a project hierarchy. Here’s a sample one for you:

Hierarchical quotas are assigned to a parent project and applied to a child project.  This hierarchy is only 3 levels deep and only has 9 projects.  A real deployment will be much larger than this. Often, a large organization has one project per user, in addition to departmental projects like the ones shown above.

Lets assume that our local sys-admin has granted our Internal domain a quota of 100 virtual machines.  How would we enforce this.  If the user attempts to create a VM in the root project of the hierarchy (a domain IS-A project) then Nova should see that the quota for that domain is 100, and that there are currently 0 VMs, so it should create the VM.  The second time this happens, there is a remaining quota of 99, and so on.

Now, lets assume that the quota is stored in Keystone, as in the current proposal we were discussing.  When Nova asks Keystone what is the quoat for “Internal” Keystone can return 100.  Nova can then query all VMs to find out which have a project ID that matches that of “Internal” and verify that there are 2. Since 100 – 2 > 0, Nova should create the VM.

What if the user wants to create a VM in the “Sales” project?  That is where things get hierarchical.  We discussed schemes where the quota would be explicitly assigned to Sales and where the quota was assumed to come from “Internal.”  Both are tricky.

Lets say we allow the explicit allocation of quota from higher to lower.  Does this mean that the parent project is reducing its own quota while creating an explicit quota for the lower project?  Or does it mean that both quotas need to be enforced?  If the quota for sales is set to 10, and the quota for the three node projects are all set to 10, is this legal or an error?

Lets assume, for a moment, that it is legal.  Under this scheme, a user with a token scoped to TestingA create 10 projects. As each project is created, Nova needs to check the number of machines already created in project TestingA.  It also needs to check the number of machines in project StagingA, ProductionA, and Sales to ensure that the quota for “Sales” has not been exceeded.  If the is an explicit quota on “Internal”, Nova needs to check the number of VMs created in that project and any project under it.  Our entire tree must be searched and counted and that count compared with the parent project.

Ideally, we would only ever have to check the quota for a single project.  That only works if:

  1. Every project in the whole tree has an explicit quota
  2. Quotas can be “split” amongst child projects but never reclaimed.

If that second statement seems strong, assume the “Marketing”  project with a quota of 10 chips off 9 for TestingB, creates 5 VMs, drops the quota for TestingB to 0, Sets the quota for StagingB to 9, and creates 9 VMs in that project.  This leaves it with 18 VMs running but only an explicit quota of 10.

The word “never” really is too strong, but it would require some form of reconcilliation process, by which Nova confirmed that both projects were within the end-state limits.

Automated Reconciliation is hard.  Keystone needs to know how to query random quanties on remote objects, and it probably should not even have acceess to those objects.  Or, Nova (and every other service using Quotas) needs to provide an API for keystone to query to confirm resources have been freed.

Manual reconcilliation is probably possible, but will be labor intensive.

One possibility is that Keystone actually record the usage of quotas, as well as the freeing of actual resources.  This is also painful, as now every single call that either creates or deletes a resource requires an additional call to Keystone.  Or, If quotas are “Batch” fetched by Nova, Nova needs to remember them, and store them locally.  If quotas then  change in Keystone, the cache is invalid.

This is only a fragment of the whole discussion.

Quotas are hard.

Using the OPTIONS Verb for RBAC

Lets say you have  RESTful Web Service.  For any given URL, you might support one or more of the HTTP verbs:  GET, PUT, POST, DELETE and so on.  A user might wonder what they mean, and which you actually support.  One way of reporting that is by using the OPTION Verb.  While this is a relatively unusual verb, using it to describe a resource is a fairly well known mechanism.  I want to take it one step further.

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Barely Functional Keystone Deployment with Docker

My eventual goal is to deploy Keystone using Kubernetes. However, I want to understand things from the lowest level on up. Since Kubernetes will be driving Docker for my deployment, I wanted to get things working for a single node Docker deployment before I move on to Kubernetes. As such, you’ll notice I took a few short cuts. Mostly, these involve configuration changes. Since I will need to use Kubernetes for deployment and configuration, I’ll postpone doing it right until I get to that layer. With that caveat, let’s begin.
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