Syncing SVN Repo's, Step by Step.

As mentioned in a previous post, I've been playing with Trac etc lately, so I've been doing some more advanced SVN work while I'm there. It's my Source Control system of choice, so I should probably learn how to use it correctly!

For posterity, here's how I've configured a sync of one SVN repo to another.... you might do this for testing an existing repo against a new tool on another machine (like my Trac VM efforts the other day), or as a warm-standby in the event of server failure etc.

Some assumptions: I'm not using Apache to run the local server, I've always used the path of least resisitance and just used svnserve.exe... either directly via the -d (daemon) flag, or as a windows service.

We're going to sync the remote (source) repo (which lives at svn://192.168.1.1) with a local (target) repo, using the built in svnsync tool. This tool doesn't like any other user changing the target repo once it's initialised, so we're only going to allow a single user access to the target.

1. Create the new local, target repository. svnsync requires a totally blank repo to start with... this means if you use Buildix and you've created a new project, you're out of luck because it initialises the repo to revision 1, due to the default folder structure. You'll need to blat the repo off disk and create it again.

svnadmin create D:\SVN_REPO

2. Configure the users/permissions on the target repo:
2.1 Change conf\svnserve.conf to include the following:

anon-access = read
auth-access = write
password-db = passwd

You can alter this as you need to, but these are the defaults... for some reason unless I uncommented these lines, my svn didn't want to honour the defaults... YMMV.

2.2 Add a user to the local repo for the sync process to run as. svnsync actually pumps the data into your repo using the normal svn API, so it needs a user to connect as. Alter passwd to include a new user:

svnsyncuser = svnsyncpassword

3. Configure the repository hooks. svnsync requires a pre-revprop-change hook to be in place, here's the simplest version:
3. 1 go to hooks
3.2 Create a couple of new files called pre-revprop-change.bat and pre-commit.bat
3.3 Alter the contents to be "return 0" <- that's a number zero
3.4 This tells the hooks to do nothing, but return success (code 0)

There's nothing to stop you doing more advanced hooks to ensure it's only the allowed user making repo changes etc if you want, but I'm K'ingISS.

4. Create a new user in the remote/source repo, using the same username/password as our freshly created user from Step 2 above.

This may not be needed, but it saves security issues around using one account to connect remotely, and another to connect locally. I have access to the remote repo, so I'm going to use it :)

5. It's time to initialise the sync!!
5.1 Stop any locally running SVN server process (apache or svnserve)... this is important
5.2 run the following command:
D:\>svnsync init file:///SVN_Repo svn://192.168.1.1/ --username svnsyncuser --password svnsyncpassword

Note that we used the file:// protocol to point to the repo, which exists at /SVN_Repo from where we ran the command (D:\). We also pass in the remote repo, and the user/pw to connect as.

If this goes smoothly, you should see "Copied properties for revision 0.".

6. At this point we can start up the local SVN Server (daemon mode, rooted at our repo):
start svnserve -d -r d:\SVN_REPO

7. Time to make initial sync, this is where all the hard work pays off!
svnsync sync svn://localhost --username svnsyncuser --password svnsyncpassword

This may take a while, as it propagates each revision from the source to the target one at a time.

To keep the repo in sync, you can either run the svnsync sync command in a bat script (using at, Scheduled Tasks etc), or configure a post-commit hook on the source repo as described at this really handy tutorial.

Remember you're dealing with Source Control, the single most important element of a software project... take backups before you start, and think before running any command that alters data to ensure you're running it on the right server etc.

Enjoy :)