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git's builtin facilities

subtree merge strategy

  • setup involves a number of different commands/options: annoying
  • cloning a repo with subtrees requires re-registration of remote branches
  • no opting out of registered dependencies--one nicety of submodules
  • dependencies must be embedded in superproject: bloat fail
  • praised for 'less, long-term administrative burden': given the simplicity of the end result, i believe it.
  • compatible with all versions of git (submodules were introduced in 1.5.3)
  • not well-advertised... why didn't i know about this feature before?

submodules

  • initizialize submodule facility, {add,update}, notice extra step
  • dependencies pulled in at a specific commit (vs. a branch head), detached from tree: very annoying
  • updating a project's submodules auto cleans the current branch: annoying
  • removing registered submodules is a real pain in the ass, and can have mixed results
  • changes to the submodule must be published before changes to the project that references it. if you forget, the repo will no longer be cloneable... fail.
  • chaos can also ensue with normal workflows: http://rubyurl.com/Umhn
  • dependencies can be individually imported into a {cloned,forked} project after registration
  • capistrano comes with builtin, hassle-free support, but at the cost of having your deployment rely on (more) external servers

git wrappers

Tim Dysinger's subtree merge sake tasks

  • pastie didn't work for me, so i created a new one here
  • simple to use, simple to setup
  • outdated and in need of updating for git 1.6.x

Pat Maddox's giternal

  • dependencies configured via repo url/path entries in config/giternal.yml
  • did not work as advertised (giternal update) out of the box--err, installing from rubygems
  • hand installing the master did, however
  • a great fit for dependencies that you have commit access to
  • push/pull changes, freeze for deploy, unfreeze for updates
  • can also be used for the simpler, track-and-update use case as well
  • read this thread for clarification of use cases, differences from braid
  • uses repository cloning and pulling in conjunction with ignore entries
  • lacks the ability to import a dep at a stable version (master branch only)
  • deploying with a known-stable version of a dependency is manual, but not a non-issue: manually change to desired branch, freeze, deploy

François Beausoleil's piston

  • made maintaining forked subversion deps a cinch before git took over... at the cost of speed
  • scm-agnostic rewrite still in the works... been a while (project initially debuted in 2006)
  • still very rough around the edges: status call blows up
  • minor gripe: some command names remain stuck in the past. e.g., {un,}locking vs. {un,}freezing
  • most of documentation is still geared for the 1.4.x (svn) generation: fail

Cristi Balan's braid

  • feature set similar to piston, but works exclusively with git
  • direct competition to François Beausoleil's piston (remember that one?)
  • can manage both git- and svn-based dependencies
  • allows for complete control (add, update, delete) of dependencies, with more features planned for 0.6
  • appears to be a wrapper for git's subtree merge strategy: yes
  • embeds dependencies in project: possible fail for larger projects (used in conjunction with FastRemoteCache, however...)
  • maintains its own, clearly named remote branches for the dependencies it manages
  • straightforward and intuitive to use
  • handy rails plugin shorthand: braid add <repo_url> -p
  • on update, halts on most operations if branches are dirty: awesome
  • deletion of deps doesn't clean up their remote branches, yet
  • no support for sending changes upstream to dependencies, a la giternal
  • dependency status planned but not been implemented yet
  • can select mirrors that also import their whole history in the parent project (handy in the case of a shared models setup)

Miles Georgi's externals

  • yet another scm-agnostic approach like piston and braid
  • royal pain: --help all but requires piping to a pager
  • {checkout,export,status,update} and {co,ex,st,up} have different behavior: confusing and unintuitive. what happened to shorthand?
  • takes agnostic to the project-level, although other project types haven't been implemented yet
  • installation shorthand driven by project type (e.g., ext install would install into vendor/plugins for a rails project)
  • shows status for all dependencies or a specific one if specified
  • deletion doesn't clean out .gitignore or .externals yet
  • built with deployment in mind: export functionality
  • clever, unusual options such as a touch_emptydirs (for forcing git to track an empty dir)
  • hasn't seen any activity for a while

symlinking

37Signals' Cached Externals

  • operates under the assumption that your dependencies won't change often... so why copy them with each deployment?
  • trivial to install: script/plugin install git://github.com/37signals/cached_externals.git
  • after that, dependencies are configured in config/externals.yml
  • path, repository URL and revision are required (shorthand for revisions is supported, but can slow down the process)
  • setup via capistrano, established locally via cap local externals:setup
  • updating is trivial: updated the desired revision and execute the setup recipe again
  • ignore rules must be set manually
  • script/generate has issues with symlinks? did not detect generators from symlinked plugins

server-side (the other half)

deploying

  • all of the approaches support (minus cached externals) some form of {copy,export}ing their managed dependencies:
    • git submodules: pulled from various remote repositories (set :git_enable_submodules, 1 in capistrano; initialization, update :web_command in vlad)
    • git subtree merge strategy and braid embed dependencies in project, and require no extra steps
    • giternal and piston: freeze dependencies, call to update in deployment script
    • ext: ext --workdir=#{current_release} ex

37 Signals' Fast Remote Cache

  • custom Capistrano deployment option that hard links the project's assets instead of copying them
  • intended for larger projects where copy time noticeably slows deployment
  • not a standalone solution: use in conjunction with any of the above options

Viget Labs' RSync with Remote Cache

  • another alternative to the standard, :remote_cache deployment option in Capistrano
  • see github page for more details

resources