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Opened 6 years ago

Last modified 6 weeks ago

#11339 new enhancement

Swappable Configuration implementations

Reported by: ethan.jucovy@… Owned by:
Priority: normal Milestone: next-dev-1.5.x
Component: general Version:
Severity: normal Keywords: config
Cc: Jun Omae, Ryan J Ollos, mael.lavault@… Branch:
Release Notes:
API Changes:

Description (last modified by Jun Omae)

On some systems, it may be useful to initialize the Trac Environment with a non-standard Configuration object. Use cases include:

  • Deploying Trac on Heroku with configuration from environment variables instead of trac.ini. Heroku provides an ephemeral filesystem; directly writing changes to files (vs. updating files locally in a git repository and pushing those changes to your Heroku instance) is risky, because those changes may disappear at any time (e.g. when redeploying code or when Heroku decides to reboot a system) and are not shared across application instances if you scale up your deployment. Meanwhile, Heroku *does* provide a persistent environment variable layer that can store up to 16kb of data. For a Heroku Trac deployment, a Configuration class that reads and writes its values via a JSON-structured environment variable would be more appropriate than a file-based configuration.
  • Preventing through-the-web changes to the configuration altogether to ensure that formatting and comments in a hand-edited trac.ini are not lost, until #7378 is closed.
  • Ensuring that trac.ini remains version-controlled by extending Configuration.save()to write out a diff from the previous file, or to commit changes directly to a repository in a subprocess.

See [Trac-dev] Setting database string from environmental variable?" for motivation.

Attachments (1)

T11339_config_from_env_vars.diff (5.4 KB ) - added by Peter Suter 2 years ago.

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Change History (12)

comment:1 by Jun Omae, 6 years ago

Cc: Jun Omae added
Description: modified (diff)
Keywords: config added
Milestone: next-major-releases

comment:2 by Ryan J Ollos, 5 years ago

One possibility might be to keep the file-based configuration and allow other configuration data sources to be specified as parents that can override the base configuration. This could be through the [inherit] section, where we currently only allow files to be specified as parents. A syntax with data source type as the prefix could allow the Configuration objects to be generated in a factory. For example, [inherit] source = osenv:trac_config, and trac_config might be an environment variable with JSON-structured content like Ethan suggested. There are many details to work out though, such as determining how the Configuration object knows to re-read the configuration data in absence of a file timestamp to check. At this point it looks like the Configuration class needs to be effectively redesigned to support data sources other than a file via ConfigParser.

comment:3 by Ryan J Ollos, 5 years ago

Cc: Ryan J Ollos added

comment:4 by Ryan J Ollos, 5 years ago

See also related ticket #11675, which would help with deployment on platforms such as Heroku.

in reply to:  description comment:5 by Ryan J Ollos, 5 years ago

Replying to ethan.jucovy@…:

  • Ensuring that trac.ini remains version-controlled by extending Configuration.save()to write out a diff from the previous file, or to commit changes directly to a repository in a subprocess.

Sending a notification on configuration change is another use-case that I'm interested in. We'll need an IConfigurationChangeListener ExtensionPoint. Configuration is not a Component though. At a minimum we will need to pass the Environment object to Configuration.

Once the extension point is implemented, an IConfigurationChangeListener can prepare a diff using the context_diff function in difflib and send a notification.

Last edited 5 years ago by Ryan J Ollos (previous) (diff)

comment:6 by Ryan J Ollos, 5 years ago

Milestone: next-major-releasesnext-dev-1.1.x

comment:7 by Ryan J Ollos, 4 years ago

Discussion about configuring Trac for Docker using environment variables gmessage:trac-dev:09KHkId-deE/DsWHuZB52tkJ.

comment:8 by Maël Lavault <mael.lavault@…>, 4 years ago

Cc: mael.lavault@… added

comment:9 by Ryan J Ollos, 4 years ago

Milestone: next-dev-1.1.xnext-dev-1.3.x

Narrowing focus for milestone:1.2. Please move ticket to milestone:1.2 if you intend to fix it.

by Peter Suter, 2 years ago

comment:10 by Peter Suter, 2 years ago

I just remembered I had this untested experimental patch. Feel free to pick it up (or to start from scratch).

comment:11 by Ryan J Ollos, 6 weeks ago

Milestone: next-dev-1.3.xnext-dev-1.5.x

Milestone renamed

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