+|keep_cache|int|RAM, in mebibytes, to reserve for caching keep collection metadata. Default 256 MiB|
+h2(#clustertarget). arv:ClusterTarget
+
+Specify which Arvados cluster should execute a container or subworkflow, and the parent project for the container request.
+
+table(table table-bordered table-condensed).
+|_. Field |_. Type |_. Description |
+|cluster_id|string|The five-character alphanumeric cluster id (uuid prefix) where a container or subworkflow will execute. May be an expression.|
+|project_uuid|string|The uuid of the project which will own container request and output of the container. May be an expression.|
+
+h2. arv:dockerCollectionPDH
+
+This is an optional extension field appearing on the standard @DockerRequirement@. It specifies the portable data hash of the Arvados collection containing the Docker image. If present, it takes precedence over @dockerPull@ or @dockerImageId@.
+
+<pre>
+requirements:
+ DockerRequirement:
+ dockerPull: "debian:8"
+ arv:dockerCollectionPDH: "feaf1fc916103d7cdab6489e1f8c3a2b+174"
+</pre>