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VCAP Package Cache

Purpose: The package cache keeps a local pre-built copy of packages (such as
ruby gems, python packages, etc.) so that they do not need to be repeatedly
downloaded and built during application staging.


-the package cache starts up a stand-alone server that waits for
requests to load packages, implementing a simple rest interface (see server.rb).

-once a request is recieved, the source package is fetched either by downloading it (if it is
remote), or copying it from the inbox directory (if it is local).

-once fetched, the source package is built in a sandboxed context, and the resulting built contents are
 archived and stored in the cache.

-the name of the built package in the cache is a function of where it came from, remote packages
are stored by their cannonical name plus a .tgz extension e.g. thin (1.2.11)
would be stored as thin-1.2.11.tgz in the cache.

-local packages are stored by the SHA1 hash of their contents plus a .tgz extension.

Security model:

-clients of the cache are assumed to be untrusted.

-clients access the cache directly through the file system.
 clients can access cache contents, but not list them.
 consequently - to access a package a client must know either
 the content of the source package(for local packages) or the
 cannonical name (for remote packages).

-to hand a local source package to the package_cache, it is copied into the
inbox directory. the inbox security model is described in detail in (inbox.rb)

*Directory structure

all directories used by the package_cache are relative to a base directory,
/var/vcap.local/package_cache, by default.

vcap.local/package_cache/cache - is the location of cached package for use.
vcap.local/package_cache/builds - is the temporary directory where packages are built.
vcap.local/package_cache/inbox - is the 'inbox' where the client places 'vendored' packages to
be added to the cache i.e. un-built packages it already has stored locally.

Using and testing the cache.

The package cache must currently be run as root, it can be started using the
following command.

/vcap/package_cache]rvmsudo ./bin/package_cache

A full working example that exercises all features of the client can
be found in -- the package cache client is found in client.rb in the
main source repository.


A simple load tester can be found in.


invoking it without arguments will display the usage message.