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185 lines
6.2 KiB
ReStructuredText
185 lines
6.2 KiB
ReStructuredText
==========================
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Adding/Removing Monitors
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==========================
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When you have a cluster up and running, you may add or remove monitors
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from the cluster at runtime.
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Adding Monitors
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===============
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Ceph monitors are light-weight processes that maintain a master copy of the
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cluster map. You can run a cluster with 1 monitor. We recommend at least 3
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monitors for a production cluster. Ceph monitors use PAXOS to establish
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consensus about the master cluster map, so you must have an odd number of
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monitors to establish a quorum for consensus about the cluster map.
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Since monitors are light-weight, it is possible to run them on the same
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host as an OSD; however, we recommend running them on separate hosts.
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.. important:: You must have an odd number of monitors in your cluster
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to establish a quorum.
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Deploy your Hardware
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--------------------
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If you are adding a new host when adding a new monitor,
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see `Hardware Recommendations`_ for details on minimum recommendations
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for monitor hardware. To add a monitor host to your cluster, first make sure you have
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an up-to-date version of Linux installed (typically Ubuntu 12.04 precise).
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Add your monitor host to a rack in your cluster, connect it to the network
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and ensure that it has network connectivity.
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.. _Hardware Recommendations: ../../install/hardware-recommendations
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Install the Required Software
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-----------------------------
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For manually deployed clusters, you must install Ceph packages
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manually. See `Installing Debian/Ubuntu Packages`_ for details.
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You should configure SSH to a user with password-less authentication
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and root permissions.
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.. _Installing Debian/Ubuntu Packages: ../../install/debian
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For clusters deployed with Chef, create a `chef user`_, `configure
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SSH keys`_, `install Ruby`_ and `install the Chef client`_ on your host. See
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`Installing Chef`_ for details.
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.. _chef user: ../../install/chef#createuser
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.. _configure SSH keys: ../../install/chef#genkeys
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.. _install the Chef client: ../../install/chef#installchef
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.. _Installing Chef: ../../install/chef
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.. _install Ruby: ../../install/chef#installruby
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.. _adding-mon:
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Adding a Monitor (Manual)
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-------------------------
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This procedure creates a ``ceph-mon`` data directory, retrieves the monitor map
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and monitor keyring, and adds a ``ceph-mon`` daemon to your cluster. If you
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this results in an even number of daemons, you may add another monitor by
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repeating this procedure until you have an odd number of ``ceph-mon`` daemons.
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#. Create the default directory on your new monitor. ::
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ssh {new-mon-host}
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sudo mkdir /var/lib/ceph/mon/ceph-{mon-letter}
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#. Retrieve the keyring for your monitors, where ``{path}`` is the path to
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the retrieved keyring, and ``{filename}`` is the name of the file containing
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the retrieved monitor key. ::
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ceph auth get mon. -o {path}/{filename}
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#. Retrieve the monitor map, where ``{path}`` is the path to
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the retrieved monitor map, and ``{filename}`` is the name of the file containing
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the retrieved monitor monitor map. ::
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ceph mon getmap -o {path}/{filename}
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#. Prepare the data directory you just created. You must specify
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the path to the monitor map so that you can retrieve the information
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about a quorum of monitors and their ``fsid``. You must also specify
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a path to the monitor keyring::
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sudo ceph-mon -i {mon-letter} --mkfs --monmap {path}/{filename} --keyring {path}/{filename}
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#. Add a ``[mon.{letter}]`` entry for your new monitor in your ``ceph.conf`` file. ::
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[mon.c]
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host = new-mon-host
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addr = ip-addr:6789
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#. Add the new monitor to the list of monitors for you cluster (runtime). This enables
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other nodes to use this monitor during their initial startup. ::
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ceph mon add <name> <ip>[:<port>]\n";
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#. Start the new monitor and it will automatically join the cluster.
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The daemon needs to know which address to bind to, either via
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``--public-addr {ip:port}`` or by setting ``mon addr`` in the
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appropriate section of ``ceph.conf``. For example::
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ceph-mon -i newname --public-addr {ip:port}
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Removing Monitors
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=================
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When you remove monitors from a cluster, Ceph monitors use PAXOS to establish
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consensus about the master cluster map, so you must have an odd number of
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monitors to establish a quorum for consensus about the cluster map.
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Removing a Monitor (Manual)
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---------------------------
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This procedure removes a ``ceph-mon`` daemon from your cluster. If this
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procedure results in an even number of daemons, you may add or remove another
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monitor until you have an odd number of ``ceph-mon`` daemons.
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#. Stop the monitor. ::
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service ceph -a stop mon.{mon-letter}
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#. Remove the monitor from the cluster. ::
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ceph mon remove {mon-letter}
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#. Remove the monitor entry from ``ceph.conf``.
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Removing Monitors from an Unhealthy Cluster
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-------------------------------------------
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This procedure removes a ``ceph-mon`` daemon from an unhealhty cluster--i.e.,
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a cluster that has placement groups that are persistently not ``active + clean``.
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#. Identify a surviving monitor. ::
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ceph mon dump
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#. Navigate to a surviving monitor's ``monmap`` directory. ::
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ssh {mon-host}
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cd /var/lib/ceph/mon/ceph-{mon-letter}/monmap
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#. List the directory contents and identify the last commmitted map.
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Directory contents will show a numeric list of maps. ::
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ls
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1 2 3 4 5 first_committed last_committed last_pn latest
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#. Identify the most recently committed map. ::
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sudo cat last_committed
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#. Copy the most recently committed file to a temporary directory. ::
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cp /var/lib/ceph/mon/ceph-{mon-letter}/monmap/{last_committed} /tmp/surviving_map
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#. Remove the non-surviving monitors. For example, if you have three monitors,
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``mon.a``, ``mon.b``, and ``mon.c``, where only ``mon.a`` will survive, follow
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the example below::
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monmaptool /tmp/surviving_map --rm {mon-letter}
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#for example
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monmaptool /tmp/surviving_map --rm b
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monmaptool /tmp/surviving_map --rm c
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#. Stop all monitors. ::
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service ceph -a stop mon
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#. Inject the surviving map with the removed monitors into the surviving monitors.
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For example, to inject a map into monitor ``mon.a``, follow the example below::
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ceph-mon -i {mon-letter} --inject-monmap {map-path}
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#for example
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ceph-mon -i a --inject-monmap /etc/surviving_map
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