From c605750db22e0807b887beae36648131805ede3c Mon Sep 17 00:00:00 2001 From: Zac Dover Date: Tue, 16 Mar 2021 01:03:06 +1000 Subject: [PATCH] doc/cephadm: rewrite "deploying add. mons" This rewrites the section "Deploying Additional Monitors (Beyond the Default Three)" for elegance and clarity. Signed-off-by: Zac Dover --- doc/cephadm/mon.rst | 54 +++++++++++++++++++++++++++++++-------------- 1 file changed, 38 insertions(+), 16 deletions(-) diff --git a/doc/cephadm/mon.rst b/doc/cephadm/mon.rst index 7bbb1f72ce2..818368e6ef2 100644 --- a/doc/cephadm/mon.rst +++ b/doc/cephadm/mon.rst @@ -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 ** +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: