doc: Document storage-service in cache configuration
diff --git a/doc/source/using_config.rst b/doc/source/using_config.rst
index 6e9fe24..7391e93 100644
@@ -96,8 +96,8 @@
-Local cache control
Beyond deciding what directory you intend to place the cache, there are
some controls on what is cached locally and how.
@@ -121,6 +121,17 @@
# Avoid caching build trees if we don't need them
+ # Support CAS server as remote cache
+ # Useful to minimize network traffic with remote execution
+ # or to work with limited local disk space
+ url: https://cache-server.com/cas:11001
+ server-cert: server.crt
+ client-cert: client.crt
+ client-key: client.key
@@ -178,6 +189,40 @@
* ``auto``: Only cache the build trees where necessary (e.g. for failed builds)
* ``always``: Always cache the build tree.
+ An optional :ref:`service configuration <user_config_remote_execution_service>`
+ to use a *Content Addressable Storage* service as a remote cache. Write access
+ is required.
+ This service is compatible with the *storage* service offered by
+ :ref:`cache servers <config_cache_servers>`.
+ Without this option, all content is stored in the local cache. This includes
+ CAS objects from fetched sources, build outputs and pulled artifacts.
+ With this option, content is primarily stored in the remote cache and the
+ local cache is populated only as needed. E.g. ``bst artifact checkout``
+ will download CAS objects on demand from the remote cache.
+ This feature is incompatible with offline operation.
+ This is primarily useful in combination with
+ :ref:`remote execution <user_config_remote_execution>` to minimize downloads
+ of build outputs, which may not be needed locally. The elimination of
+ unnecessary downloads reduces total build time, especially if the bandwidth
+ between the local system and the remote execution cluster is limited.
+ .. tip::
+ Skip the ``storage-service`` option in the
+ :ref:`remote execution <user_config_remote_execution>` configuration to
+ use the same CAS service for caching and remote execution.
+ It is also possible to configure this with local builds without remote
+ execution. This enables operation with a small local cache even with large
+ projects. However, for local builds this can result in a longer total build
+ time due to additional network transfers. This is only recommended with a
+ high bandwidth connection to a storage-service, ideally in a local network.
@@ -932,6 +977,11 @@
This service is compatible with the *storage* service offered by
:ref:`cache servers <config_cache_servers>`.
+ This is optional if a ``storage-service`` is configured in the
+ :ref:`cache configuration <config_local_cache>`, in which case actual file
+ contents of build outputs will only be downloaded as needed, e.g. on
+ ``bst artifact checkout``.
A :ref:`service configuration <user_config_remote_execution_service>` specifying