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RADOS Dictionary Plugin

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Peter Mauritius edited this page Dec 5, 2017 · 13 revisions

Overview

The Dovecot dictionaries are a good candidate to be implemented using the Ceph omap key/value store. They are a building block to enable a Dovecot, which runs exclusively on Ceph.

Dovecot uses two namespaces for dictionary keys.

shared/<key>

These are shared entries. These keys will be stored in a RADOS object named <oid>/shared. <key> will be used as omap key as given.

priv/<key>

These are private entries for a user. These keys will be stored in a RADOS object named <oid>/<username>. <key> will be used as omap key as given.

Configuration

Dovecot

To load the plugin, add dict_rados to the list of mail plugins to be loaded. There are several ways to do this. Add for example the plugin in 10-mail.conf to mail_plugins.

mail_plugins = $mail_plugins dict_rados

To enable or disable the plugin per user, you can make your userdb return mail_plugins as an extra field. See UserDatabase/ExtraFields for examples.

The name of the dict driver is rados. Add the plugin for example to 10-mail.conf as mail\_attribute\_dict. See Dovecot Dictionaries for details.

mail_attribute_dict = rados:oid=metadata:pool=mail_dictionary

The configuration parameters are:

oid

The RADOS object id to use.

pool

The RADOS pool to use for the dictionary objects. The pool name ist optional and defaults to mail_dictionary. If the pool is missing, it will be created.

All key/values are be stored in OMAP key/values of the object <oid>.

Ceph

The plugin uses the default way for Ceph configuration described in Step 2: Configuring a Cluster Handle:

  1. rados_conf_parse_env(): Evaluate the CEPH_ARGS environment variable.

  2. rados_conf_read_file(): Search the default locations, and the first found is used. The locations are:

    • $CEPH_CONF (environment variable)

    • /etc/ceph/ceph.conf

    • ~/.ceph/config

    • ceph.conf (in the current working directory)

Testing

The source directory src/dict-rados contains a test application named test-*. They use the configuration in the same directory.

The configuration assumes a Ceph cluster running locally without cephx, that has for example been created using vstart.sh as decribed in Developer Guide (quick) or ceph/README.md.

../src/vstart.sh -X -n -l

Any other way to get a Ceph cluster is valid, too.

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