gitolite/doc/delegation.mkd

delegating access control responsibilities

[Thanks to jeromeag for forcing me to think through this...]

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In this document:

• lots of repos, lots of users
• splitting up the set of repos into groups
• delegating ownership of groups of repos
• security/philosophy note

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lots of repos, lots of users

Gitolite tries to make it easy to manage access to lots of users and repos, exploiting commonalities wherever possible. It lets you specify bits and pieces of the access control separately -- i.e., all the access specs for a certain repo need not be together; they can be scattered, which makes it easier to manage the sort of slice and dice needed in that example.

But eventually the config file will become too big. If you let only one person have control, he could become a bottleneck. If you give it to multiple people, they might make mistakes or stomp on each others' work accidentally.

The best way is to divide up the config file and give parts of it to different people.

Ideally, we would delegate authority for groups of repos, not individual repos, otherwise it doesn't scale. It would also be nice if we could prevent an admin from creating access rules for any repo in the system -- i.e., set limits on what repos he can control. This would be a nice "security" feature.

Delegation offers a way to do all that. Note that delegated admins cannot create or remove users, not can they define new repos. They can only define access control rules for a set of repos they have been given authority for.

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It's easier to show how it all works with an example instead of long descriptions.

splitting up the set of repos into groups

To start with, recall that gitolite allows you to specify groups (of users or repos, same syntax). So the basic idea is that the main config file (conf/gitolite.conf in your admin repo clone) will specify some repo groups:

# group your projects/repos however you want
@webbrowser_repos           = firefox lynx
@webserver_repos            = apache nginx
@malware_repos              = conficker storm

# any other config as usual, including access control lines for any of the
# above projects or groups

delegating ownership of groups of repos

Once the repos are grouped, give each person charge of one or more groups. For example, Alice may be in charge of all web browser development projects, Bob takes care of web servers, and Mallory, as tradition dictates, is in charge of malware ;-)

You do this by adding branches to the gitolite-admin repo:

# the admin repo access was probably like this to start with:
repo gitolite-admin
    RW+                                         = sitaram
# now add these lines to the config for the admin repo
    RW                                          = alice bob mallory
    RW+ NAME/                                   = sitaram
    RW  NAME/conf/fragments/webbrowser_repos    = alice
    RW  NAME/conf/fragments/webserver_repos     = bob
    RW  NAME/conf/fragments/malware_repos       = mallory

This uses gitolite's ability to restrict pushes by file/dir name being changed -- the syntax you see above ensures that, while "sitaram" does not have any NAME based restrictions, the other 3 users do. See conf/example.conf for syntax and notes.

As you can see, for each repo group you want to delegate authority over, there's a rule for a corresponding file in conf/fragments in the gitolite-admin repo. If you have write access to that file, you are allowed to define rules for repos in that repo group.

In other words, we use gitolite's file/dir NAME-based permissions to "enforce" the separation between the delegated configs!

Here's how to use this in practice:

• Alice clones the gitolite-admin repo, and adds a file called conf/fragments/webbrowser_repos.conf

• she writes in this file any access control rules for the "firefox" and "lynx" repos. She should not write access rules for any other project -- they will be ignored

• Alice then commits and pushes to the gitolite-admin repo

Naturally, a successful push invokes the post-update hook that the admin repo has, which eventually runs the compile script. The net effect is as if you appended the contents of all the "fragment" files, in alphabetical order, to the bottom of the main file.

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security/philosophy note

The delegation feature is meant only for access control rules, not pubkeys. Adding/removing pubkeys is a much more significant event than changing branch level permissions for people already on staff, and only the main admin should be allowed to do it.

Gitolite's "userids" all live in the same namespace. This is unlikely to change, so please don't ask -- it gets real complicated to do otherwise. Allowing delegated admins to add users means username collisions, which also means security problems (admin-A creates a pubkey for Admin-B, thus gaining access to all of Admin-B's stuff).

If you feel the need to delegate even that, please just go the whole hog and give them separate gitolite instances! It's pretty easy to setup the software itself system-wide, so that many users can use it without all the "easy install" fuss. See the "system install / user setup" section in doc/1-INSTALL.mkd for details.