doc/rgw: document placement target configuration

Fixes: http://tracker.ceph.com/issues/24508

Signed-off-by: Casey Bodley <cbodley@redhat.com>

doc/radosgw/index.rst

@@ -40,6 +40,7 @@ you may write data with one API and retrieve it with the other.
 
    Manual Install w/Civetweb <../../install/install-ceph-gateway>
    HTTP Frontends <frontends>
+   Pool Placement <placement>
    Multisite Configuration <multisite>
    Configuring Pools <pools>
    Config Reference <config-ref>

doc/radosgw/placement.rst

@@ -0,0 +1,180 @@
+==============
+Pool Placement
+==============
+
+.. contents::
+
+Placement Targets
+=================
+
+.. versionadded:: Jewel
+
+Placement targets control which `Pools`_ are associated with a particular
+bucket. A bucket's placement target is selected on creation, and cannot be
+modified. The ``radosgw-admin bucket stats`` command will display its
+``placement_rule``.
+
+The zonegroup configuration contains a list of placement targets with an
+initial target named ``default-placement``. The zone configuration then maps
+each zonegroup placement target name onto its local storage. This zone
+placement information includes the ``index_pool`` name for the bucket index,
+the ``data_extra_pool`` name for metadata about incomplete multipart uploads,
+and a ``data_pool`` name for object data.
+
+Zonegroup/Zone Configuration
+============================
+
+Placement configuration is performed with ``radosgw-admin`` commands on
+the zonegroups and zones.
+
+The zonegroup placement configuration can be queried with:
+
+::
+
+  $ radosgw-admin zonegroup get
+  {
+      "id": "ab01123f-e0df-4f29-9d71-b44888d67cd5",
+      "name": "default",
+      "api_name": "default",
+      ...
+      "placement_targets": [
+          {
+              "name": "default-placement",
+              "tags": [],
+          }
+      ],
+      "default_placement": "default-placement",
+      ...
+  }
+
+The zone placement configuration can be queried with:
+
+::
+
+  $ radosgw-admin zone get
+  {
+      "id": "557cdcee-3aae-4e9e-85c7-2f86f5eddb1f",
+      "name": "default",
+      "domain_root": "default.rgw.meta:root",
+      ...
+      "placement_pools": [
+          {
+              "key": "default-placement",
+              "val": {
+                  "index_pool": "default.rgw.buckets.index",
+                  "data_pool": "default.rgw.buckets.data",
+                  "data_extra_pool": "default.rgw.buckets.non-ec",
+                  "index_type": 0
+              }
+          }
+      ],
+      ...
+  }
+
+.. note:: If you have not done any previous `Multisite Configuration`_,
+          a ``default`` zone and zonegroup are created for you, and changes
+          to the zone/zonegroup will not take effect until the Ceph Object
+          Gateways are restarted. If you have created a realm for multisite,
+          the zone/zonegroup changes will take effect once the changes are
+          committed with ``radosgw-admin period update --commit``.
+
+Adding a Placement Target
+-------------------------
+
+To create a new placement target named ``temporary``, start by adding it to
+the zonegroup:
+
+::
+
+  $ radosgw-admin zonegroup placement add \
+        --rgw-zonegroup default \
+        --placement-id temporary
+
+Then provide the zone placement info for that target:
+
+::
+
+  $ radosgw-admin zone placement add \
+        --rgw-zone default \
+        --placement-id temporary \
+        --data-pool default.rgw.temporary.data \
+        --index-pool default.rgw.temporary.index \
+        --data-extra-pool default.rgw.temporary.non-ec \
+        --compression lz4
+
+Customizing Placement
+=====================
+
+Default Placement
+-----------------
+
+By default, new buckets will use the zonegroup's ``default_placement`` target.
+This zonegroup setting can be changed with:
+
+::
+
+  $ radosgw-admin zonegroup placement default \
+        --rgw-zonegroup default \
+        --placement-id new-placement
+
+User Placement
+--------------
+
+A Ceph Object Gateway user can override the zonegroup's default placement
+target by setting a non-empty ``default_placement`` field in the user info.
+
+::
+
+  $ radosgw-admin user info --uid testid
+  {
+      ...
+      "default_placement": "",
+      "placement_tags": [],
+      ...
+  }
+
+If a zonegroup's placement target contains any ``tags``, users will be unable
+to create buckets with that placement target unless their user info contains
+at least one matching tag in its ``placement_tags`` field. This can be useful
+to restrict access to certain types of storage.
+
+The ``radosgw-admin`` command cannot modify these fields directly, so the json
+format must be edited manually:
+
+::
+
+  $ radosgw-admin metadata get user:<user-id> > user.json
+  $ vi user.json
+  $ radosgw-admin metadata put user:<user-id> < user.json
+
+S3 Bucket Placement
+-------------------
+
+When creating a bucket with the S3 protocol, a placement target can be
+provided as part of the LocationConstraint to override the default placement
+targets from the user and zonegroup.
+
+Normally, the LocationConstraint must match the zonegroup's ``api_name``:
+
+::
+
+  <LocationConstraint>default</LocationConstraint>
+
+A custom placement target can be added to the ``api_name`` following a colon:
+
+::
+
+  <LocationConstraint>default:new-placement</LocationConstraint>
+
+Swift Bucket Placement
+----------------------
+
+When creating a bucket with the Swift protocol, a placement target can be
+provided in the HTTP header ``X-Storage-Policy``:
+
+::
+
+  X-Storage-Policy: new-placement
+
+.. _`Pools`: ../pools
+.. _`Multisite Configuration`: ../multisite