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doc/cephadm: rewrite "deploying add. mons"

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This rewrites the section "Deploying Additional
Monitors (Beyond the Default Three)" for elegance
and clarity.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
This commit is contained in:
Zac Dover 2021-03-16 01:03:06 +10:00
parent 2240a32021
commit c605750db2
1 changed files with 38 additions and 16 deletions
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54
doc/cephadm/mon.rst
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@ -4,26 +4,36 @@ MON Service
.. _deploy_additional_monitors:
Deploy additional monitors
==========================
Deploying additional monitors (beyond the default three)
========================================================
A typical Ceph cluster has three or five monitor daemons spread
across different hosts. We recommend deploying five
monitors if there are five or more nodes in your cluster.
A typical Ceph cluster has three or five monitor daemons that are spread
across different hosts. We recommend deploying five monitors if there are
five or more nodes in your cluster.
.. _CIDR: https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#CIDR_notation
When Ceph knows what IP subnet the monitors should use it can automatically
deploy and scale monitors as the cluster grows (or contracts). By default,
Ceph assumes that other monitors should use the same subnet as the first
monitor's IP.
Ceph deploys monitor daemons automatically as the cluster grows and Ceph
scales back monitor daemons automatically as the cluster shrinks. The
smooth execution of this automatic growing and shrinking depends upon
proper subnet configuration.
If your Ceph monitors (or the entire cluster) live on a single subnet,
then by default cephadm automatically adds up to 5 monitors as you add new
hosts to the cluster. No further steps are necessary.
The cephadm bootstrap procedure assigns the first monitor daemon in the
cluster to a particular subnet. ``cephadm`` designates that subnet as the
default subnet of the cluster. New monitor daemons will be assigned by
default to that subnet unless cephadm is instructed to do otherwise.
* If there is a specific IP subnet that should be used by monitors, you
can configure that in `CIDR`_ format (e.g., ``10.1.2.0/24``) with:
If all of the ceph monitor daemons in your cluster are in the same subnet,
manual administration of the ceph monitor daemons is not necessary.
``cephadm`` will automatically add up to five monitors to the subnet, as
needed, as new hosts are added to the cluster.
Designating a Particular Subnet for Monitors
============================================
To designate a particular IP subnet for use by ceph monitor daemons, use a
command of the following form, including the subnet's address in `CIDR`_
format (e.g., ``10.1.2.0/24``):
.. prompt:: bash #
@ -35,8 +45,11 @@ hosts to the cluster. No further steps are necessary.
ceph config set mon public_network 10.1.2.0/24
Cephadm deploys new monitor daemons only on hosts that have IPs
configured in the configured subnet.
Cephadm deploys new monitor daemons only on hosts that have IP addresses in
the designated subnet.
Changing the number of monitors from the default
================================================
* If you want to adjust the default of 5 monitors, run this command:
@ -44,6 +57,9 @@ hosts to the cluster. No further steps are necessary.
ceph orch apply mon *<number-of-monitors>*
Deploying monitors only to specific hosts
=========================================
* To deploy monitors on a specific set of hosts, run this command:
.. prompt:: bash #
@ -52,6 +68,9 @@ hosts to the cluster. No further steps are necessary.
Be sure to include the first (bootstrap) host in this list.
Using Host Labels
=================
* You can control which hosts the monitors run on by making use of
host labels. To set the ``mon`` label to the appropriate
hosts, run this command:
@ -90,6 +109,9 @@ hosts to the cluster. No further steps are necessary.
ceph orch apply mon label:mon
Deploying Monitors Manually
===========================
* You can explicitly specify the IP address or CIDR network for each monitor
and control where it is placed. To disable automated monitor deployment, run
this command: