Default templates for each plugin

Default templates for each plugin

Blueprint: https://blueprints.launchpad.net/sahara/+spec/default-templates

In order to create a basic cluster for any plugin, a user currently has to go through several steps to create an appropriate set of node group and cluster templates. We believe that set of actions should be captured in a default set of templates (per plugin) and loaded into the database ahead of time so that users do not need to repeat some of the most basic steps to provision a simple cluster.

Problem description

Creating even a basic cluster currently requires several steps before the user is able to launch their cluster. In an effort to reduce the amount of effort and time to get a simple cluster running, we propose a set of default templates for each plugin that will be pre-loaded and available for use.

Other potential issues/answers: 1) How do we make the set of templates available for all users/tenants? Today, any given template is only read/writable by one tenant.

A) Implement ACL support for templates (SLukjanov plans to write the spec for this). Having proper ACL support in place will allow us to manage access for read/write across all tenants.

ACL support is not available yet. For the time being, templates will be added per-tenant.

2) Do we allow editing of default templates? I don’t think we should allow editing of the default templates since they are shared among all tenants. The flow to “edit” one would be to make a copy of the template and work from there. I propose that each template will be stored with a flag in the database that identifies each default template as being a default template so that we can enforce that users cannot change the default templates.

3) How do we avoid uploading the same default templates each time at startup while still allowing for them to be updated as necessary? We could use a numbering system in the template file names to indicate the version number and store that in the database (perhaps instead of a boolean flag indicating that the template is a default template, we could store an int that is the version number). At startup time, we would go through all of the template files for each plugin and compare the version numbers to the version numbers that are stored in the database.

Sqlalchemy will detect when fields have changed and set the “updated at” field accordingly. Therefore, we can simply attempt to update existing templates whenever the script is run. If the template matches what is in the database, there will be no update.

4) How do we make a json default cluster template reference a json default node group template since we won’t know the node group template IDs?

A) CLI util will operate them one-by-one starting with node group templates and then cluster templates. In addition, we could create a few example jobs that could be used for health check.

Proposed change

  1. Create sets of default template json files for each plugin.

    A set of default templates will consist of node group templates and/or cluster templates. Whether or not a template file defines a node group template or a cluster template will be determined based on the presence of required fields specified in the Sahara JSON validation code. Node group templates require flavor_id and node_processes, so presence of these fields implicitly identify a template as a node group template. If it is not a node group template, it is a cluster template. This identification avoids a naming scheme or some other kind of extra labeling to identify a template type.

    Default templates distributed with Sahara will be located in sahara/plugins/default_templates/. The code that processes the default templates should use this path as a default starting point but should allow a different starting point to be specified. It should make no assumptions about the directory structure beyond the following:

    • All of the template files in a particular directory should be treated as a set, and cluster templates may reference node group templates in the same set by name.
    • Directories may be nested for logical organization, so that a plugin may define default template sets for each version. Therefore, the code should recurse through subdirectories by default but it should be possible to specify no recursion.

    This design will allow code to process default templates decoupled from explicit knowledge of Sahara plugins, plugin versions, or the structure of plugin directories. The ability to specify a different starting point will allow a user to process particular template sets if the entire set is not desired (only some plugins enabled, for instance), or if an alternate set at a different location is desired. In short, it keeps the processing general and simple.

    In practice, the directories under sahara/plugins/default_templates will be named for plugins, and subdirectories will be created for different versions as appropriate.

  2. Add a CLI util that can be executed by cron with admin credentials to create/update existing default templates. This utility needs to be able to take some placeholders like “flavor” or “network” and make the appropriate substitutions (either from configs or via command line args) at runtime. The cron job can be optional if we want to force any updates to be triggered explicitly.

    The CLI will take an option to specify the starting directory (default will be sahara/plugins/default_templates).

    The CLI will take an option to disable recursion through subdirectories (default will be to recurse).

    At a minimum, the CLI will provide a command to create or update default templates with processing beginning at the designated starting directory.

    The CLI should use the “plugins” configuration parameter from the [database] section to filter the templates that are processed. If the “plugin-name” field of a template matches a plugin name in the “plugins” list, it will be processed. If the “plugins” list is empty, all templates will be processed. It should be possible to override the “plugins” configuration from the command line with a “–plugin-name” option.

    If there is an error during updating or creating templates in a particular set, the CLI should attempt to undo any modifications or creations that were done as part of that set.

    The CLI should also provide a mechanism for deleting default templates, since the is_default field will prevent that, should an admin for some reason desire to remove default templates. This can be a simple operation that will remove a single default template by ID. It is not likely to be used very often.

Alternatives

1) The loading process could be done via the REST API if we wanted to have some sort of external process that manages the default templates. That might require changing the API a bit to add endpoints for managing the default templates and seems like a fair bit of unnecessary work since the management of default templates should be something done only within Sahara.

2) Add a hook, possibly in plugins/base:PluginManager for “load_default_templates”. This method would be responsible for triggering the loading of the defaults at startup time.

Data model impact

N/A

REST API impact

N/A

Other end user impact

End users will see the default templates show up just like any other template that they may have created.

Deployer impact

N/A

Developer impact

N/A

Sahara-image-elements impact

N/A

Sahara-dashboard / Horizon impact

N/A The default templates will show-up in the UI and look like regular templates.

Implementation

Assignee(s)

Primary assignee:
croberts
Secondary assignee:
tmckay

Work Items

1) Come up with a set of default templates for each plugin. These will probably be json formatted files.

2) Come up with some sort of mechanism to load the templates or ensure that they are already loaded when Sahara starts-up.

  1. Update the Sahara documentation.

Dependencies

1) Implementation of the ACL for templates (spec still TBD). This will let us give all users read access to the default templates while still possibly allowing admins to edit the templates.

Testing

Ideally, tests will be added to ensure that a functioning cluster can be started based on each of the default template sets. If that is determined to be too time-consuming per-run, then tests to ensure the validity of each set of templates may be sufficient.

Documentation Impact

The Sahara documentation should be updated to note that the default templates are available for use. Additionally, any future plugins will be expected to provide their own set of default templates.

References

N/A

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

sahara-specs 0.0.1.dev337