Replication Configuration

Enabling Replication

If replicating over SSH, ensure the host key of the remote system(s) is already in the Gerrit user's ~/.ssh/known_hosts file. The easiest way to add the host key is to connect once by hand with the command line:

  sudo su -c 'ssh echo' gerrit2
  [remote "host-one"]
    url =${name}.git

  [remote "pubmirror"]
    url =${name}.git
    url =${name}.git
    url =${name}.git
    push = +refs/heads/*:refs/heads/*
    push = +refs/tags/*:refs/tags/*
    threads = 3
    authGroup = Public Mirror Group
    authGroup = Second Public Mirror Group

Then reload the replication plugin to pick up the new configuration:

  ssh -p 29418 localhost gerrit plugin reload replication

To manually trigger replication at runtime, see SSH command start.

File replication.config

The optional file $site_path/etc/replication.config is a Git-style config file that controls the replication settings for the replication plugin.

The file is composed of one or more remote sections, each remote section provides common configuration settings for one or more destination URLs.

Each remote section uses its own thread pool. If pushing to multiple remotes, over differing types of network connections (e.g. LAN and also public Internet), its a good idea to put them into different remote sections, so that replication to the slower connection does not starve out the faster local one. The example file above does this.

In the keys below, the NAME portion is unused by this plugin, but must be unique to distinguish the different sections if more than one remote section appears in the file.

gerrit.replicateOnStartup : If true, replicates to all remotes on startup to ensure they are in-sync with this server. By default, true.

gerrit.autoReload : If true, automatically reloads replication destinations and settings after replication.config file is updated, without the need to restart the replication plugin. When the reload takes place, pending replication events based on old settings are discarded. By default, false.

gerrit.defaultForceUpdate : If true, the default push refspec will be set to use forced update to the remote when no refspec is given. By default, false.

replication.lockErrorMaxRetries : Number of times to retry a replication operation if a lock error is detected.

If two or more replication operations (to the same GIT and Ref)
are scheduled at approximately the same time (and end up on different
replication threads), there is a large probability that the last
push to complete will fail with a remote "failure to lock" error.
This option allows Gerrit to retry the replication push when the
"failure to lock" error is detected.

A good value would be 3 retries or less, depending on how often
you see lockError collisions in your server logs. A too highly set
value risks keeping around the replication operations in the queue
for a long time, and the number of items in the queue will increase
with time.

Normally Gerrit will succeed with the replication during its first
retry, but in certain edge cases (e.g. a mirror introduces a ref
namespace with the same name as a branch on the master) the retry
will never succeed.

The issue can also be mitigated somewhat by increasing the

Default: 0 (disabled, i.e. never retry)

replication.maxRetries : Maximum number of times to retry a push operation that previously failed.

When a push operation reaches its maximum number of retries,
the replication event is discarded from the queue and the remote
destinations may remain out of sync.

Can be overridden at remote-level by setting replicationMaxRetries.

By default, pushes are retried indefinitely.

remote.NAME.url : Address of the remote server to push to. Multiple URLs may be specified within a single remote block, listing different destinations which share the same settings. Assuming sufficient threads in the thread pool, Gerrit pushes to all URLs in parallel, using one thread per URL.

Within each URL value the magic placeholder `${name}` is
replaced with the Gerrit project name.  This is a Gerrit
specific extension to the otherwise standard Git URL syntax
and it must be included in each URL so that Gerrit can figure
out where each project needs to be replicated. `${name}` may
only be omitted if the remote refers to a single repository
(i.e.: Exactly one [remote.NAME.projects][3] and that name's
value is a single project match.).

See [git push][1] for details on Git URL syntax.

remote.NAME.adminUrl : Address of the alternative remote server only for repository creation. Multiple URLs may be specified within a single remote block, listing different destinations which share the same settings.

The adminUrl can be used as an ssh alternative to the url
option, but only related to repository creation.  If not
specified, the repository creation tries to follow the default
way through the url value specified.

It is useful when the remote.NAME.url protocols do not allow
repository creation although their usage is mandatory in the
local environment.  In that case, an alternative SSH url could
be specified to repository creation.

To enable replication to different Gerrit instance use `gerrit+ssh://`
as protocol name followed by hostname of another Gerrit server eg.


In this case replication will use Gerrit's SSH API to
create/remove projects and update repository HEAD references.

NOTE: In order to replicate project deletion, the
link: delete-project[delete-project]
plugin must be installed on the other Gerrit.

remote.NAME.receivepack : Path of the git-receive-pack executable on the remote system, if using the SSH transport.

Defaults to `git-receive-pack`.

remote.NAME.uploadpack : Path of the git-upload-pack executable on the remote system, if using the SSH transport.

Defaults to `git-upload-pack`.

remote.NAME.push : Standard Git refspec denoting what should be replicated. Setting this to +refs/heads/*:refs/heads/* would mirror only the active branches, but not the change refs under refs/changes/, or the tags under refs/tags/.

Note that prefixing a source refspec with `+` causes the replication
to be done with a `git push --force` command.
Be aware that when you are pushing to remote repositories that may
have read/write access (e.g. GitHub) you may want to omit the `+`
to prevent the risk of overwriting branches that have been modified
on the remote.

Multiple push keys can be supplied, to specify multiple
patterns to match against.  In the [example above][2], remote
"pubmirror" uses two push keys to match both `refs/heads/*`
and `refs/tags/*`, but excludes all others, including

Defaults to `refs/*:refs/*` (push all refs) if not specified,
or `+refs/*:refs/*` (force push all refs) if not specified and
`gerrit.defaultForceUpdate` is true.

Note that the `refs/meta/config` branch is only replicated
when `replicatePermissions` is true, even if the push refspec
is 'all refs'.

remote.NAME.timeout : Number of seconds to wait for a network read or write to complete before giving up and declaring the remote side is not responding. If 0, there is no timeout, and the push client waits indefinitely.

A timeout should be large enough to mostly transfer the
objects to the other side.  1 second may be too small for
larger projects, especially over a WAN link, while 10-30
seconds is a much more reasonable timeout value.

Defaults to 0 seconds, wait indefinitely.

remote.NAME.replicationDelay : Time to wait before scheduling a remote push operation. Setting the delay to 0 effectively disables the delay, causing the push to start as soon as possible.

This is a Gerrit specific extension to the Git remote block.

By default, 15 seconds.

remote.NAME.rescheduleDelay : Delay when rescheduling a push operation due to an in-flight push running for the same project.

Cannot be set to a value lower than 3 seconds to avoid a tight loop
of schedule/run which could cause 1K+ retries per second.

A configured value lower than 3 seconds will be rounded to 3 seconds.

By default, 3 seconds.

remote.NAME.replicationRetry : Time to wait before scheduling a remote push operation previously failed due to an offline remote server.

If a remote push operation fails because a remote server was
offline, all push operations to the same destination URL are
blocked, and the remote push is continuously retried unless
the replicationMaxRetries value is set.

This is a Gerrit specific extension to the Git remote block.

By default, 1 minute.

remote.NAME.replicationMaxRetries : Maximum number of times to retry a push operation that previously failed.

When a push operation reaches its maximum number of retries
the replication event is discarded from the queue and the remote
destinations could be out of sync.

This is a Gerrit specific extension to the Git remote block.

By default, use replication.maxRetries.

remote.NAME.threads : Number of worker threads to dedicate to pushing to the repositories described by this remote. Each thread can push one project at a time, to one destination URL. Scheduling within the thread pool is done on a per-project basis. If a remote block describes 4 URLs, allocating 4 threads in the pool will permit some level of parallel pushing.

By default, 1 thread.

remote.NAME.authGroup : Specifies the name of a group that the remote should use to access the repositories. Multiple authGroups may be specified within a single remote block to signify a wider access right. In the project administration web interface the read access can be specified for this group to control if a project should be replicated or not to the remote.

By default, replicates without group control, i.e. replicates
everything to all remotes.

remote.NAME.createMissingRepositories : If true, a repository is automatically created on the remote site. If the remote site was not available at the moment when a new project was created, it will be created if during the replication of a ref it is found to be missing.

If false, repositories are never created automatically on this

By default, true, missing repositories are created.

remote.NAME.replicatePermissions : If true, permissions-only projects and the refs/meta/config branch will also be replicated to the remote site. These projects and branches may be needed to keep a backup or slave server current.

By default, true, replicating everything.

remote.NAME.replicateProjectDeletions : If true, project deletions will also be replicated to the remote site.

By default, false, do *not* replicate project deletions.

remote.NAME.replicateHiddenProjects : If true, hidden projects will be replicated to the remote site.

By default, false, do *not* replicate hidden projects.

remote.NAME.mirror : If true, replication will remove remote branches that are absent locally or invisible to the replication (for example read access denied via authGroup option).

By default, false, do not remove remote branches.

remote.NAME.remoteNameStyle : Provides possibilities to influence the name of the target repository, e.g. by replacing slashes in the ${name} placeholder.

Github and Gitorious do not permit slashes "/" in repository
names and will change them to dashes "-" at repository creation

If this setting is set to "dash", slashes will be replaced with
dashes in the remote repository name. If set to "underscore",
slashes will be replaced with underscores in the repository name.

Option "basenameOnly" makes `${name}` to be only the basename
(the part after the last slash) of the repository path on the
Gerrit server, e.g. `${name}` of `foo/bar/my-repo.git` would
be `my-repo`.

By default, "slash", i.e. remote names will contain slashes as
they do in Gerrit.

remote.NAME.projects : Specifies which repositories should be replicated to the remote. It can be provided more than once, and supports three formats: regular expressions, wildcard matching, and single project matching. All three formats match case-sensitive.

Values starting with a caret `^` are treated as regular
expressions. `^foo/(bar|baz)` would match the projects
`foo/bar`, and `foo/baz`. Regular expressions have to fully
match the project name. So the above example would not match
`foo/bar2`, while `^foo/(bar|baz).*` would.

Projects may be excluded from replication by using a regular
expression with inverse match. `^(?:(?!PATTERN).)*$` will
exclude any project that matches.

Values that are not regular expressions and end in `*` are
treated as wildcard matches. Wildcards match projects whose
name agrees from the beginning until the trailing `*`. So
`foo/b*` would match the projects `foo/b`, `foo/bar`, and
`foo/baz`, but neither `foobar`, nor `bar/foo/baz`.

Values that are neither regular expressions nor wildcards are
treated as single project matches. So `foo/bar` matches only
the project `foo/bar`, but no other project.

By default, replicates without matching, i.e. replicates
everything to all remotes.

File secure.config

The optional file $site_path/secure.config is a Git-style config file that provides secure values that should not be world-readable, such as passwords. Passwords for HTTP remotes can be obtained from this file.

remote.NAME.username : Username to use for HTTP authentication on this remote, if not given in the URL.

remote.NAME.password : Password to use for HTTP authentication on this remote.

File ~/.ssh/config

If present, Gerrit reads and caches ~/.ssh/config at startup, and supports most SSH configuration options. For example:

    IdentityFile ~/.ssh/id_hostone
    PreferredAuthentications publickey

  Host mirror*
    User mirror-updater
    IdentityFile ~/.ssh/id_pubmirror
    PreferredAuthentications publickey

Supported options:

  • Host
  • Hostname
  • User
  • Port
  • IdentityFile
  • PreferredAuthentications
  • StrictHostKeyChecking

SSH authentication must be by passwordless public key, as there is no facility to read passphrases on startup or passwords during the SSH connection setup, and SSH agents are not supported from Java.

Host keys for any destination SSH servers must appear in the user's ~/.ssh/known_hosts file, and must be added in advance, before Gerrit starts. If a host key is not listed, Gerrit will be unable to connect to that destination, and replication to that URL will fail.