Installation (cephadm)


The cephadm bootstrap feature is first introduced in Octopus, and is not yet recommended for production deployments.

A new Ceph cluster is deployed by bootstrapping a cluster on a single node, and then adding additional nodes and daemons via the CLI or GUI dashboard.

The following example installs a basic three-node cluster. Each node will be identified by its prompt. For example, “[monitor 1]” identifies the first monitor, “[monitor 2]” identifies the second monitor, and “[monitor 3]” identifies the third monitor. This information is provided in order to make clear which commands should be issued on which systems.

“[any node]” identifies any Ceph node, and in the context of this installation guide means that the associated command can be run on any node.

Get cephadm

The cephadm utility is used to bootstrap a new Ceph Cluster.

Use curl to fetch the standalone script:

[monitor 1] # curl --silent --remote-name --location
[monitor 1] # chmod +x cephadm

You can also get the utility by installing a package provided by your Linux distribution:

[monitor 1] # apt install -y cephadm   # or
[monitor 1] # dnf install -y cephadm   # or
[monitor 1] # yum install -y cephadm   # or
[monitor 1] # zypper install -y cephadm

Bootstrap a new cluster

To create a new cluster, you need to know:

  • Which IP address to use for the cluster’s first monitor. This is normally just the IP for the first cluster node. If there are multiple networks and interfaces, be sure to choose one that will be accessible by any hosts accessing the Ceph cluster.

To bootstrap the cluster run the following command:

[node 1] $ sudo ./cephadm bootstrap --mon-ip *<mon-ip>*

This command does a few things:

  • Creates a monitor and manager daemon for the new cluster on the local host. A minimal configuration file needed to communicate with the new cluster is written to ceph.conf in the local directory.

  • A copy of the client.admin administrative (privileged!) secret key is written to ceph.client.admin.keyring in the local directory.

  • Generates a new SSH key, and adds the public key to the local root user’s /root/.ssh/authorized_keys file. A copy of the public key is written to in the local directory.

Interacting with the cluster

To interact with your cluster, start up a container that has all of the Ceph packages installed:

[any node] $ sudo ./cephadm shell --config ceph.conf --keyring ceph.client.admin.keyring

The --config and --keyring arguments will bind those local files to the default locations in /etc/ceph inside the container to allow the ceph CLI utility to work without additional arguments. Inside the container, you can check the cluster status with:

[ceph: root@monitor_1_hostname /]# ceph status

In order to interact with the Ceph cluster outside of a container (that is, from the command line), install the Ceph client packages and install the configuration and privileged administrator key in a global location:

[any node] $ sudo apt install -y ceph-common   # or,
[any node] $ sudo dnf install -y ceph-common   # or,
[any node] $ sudo yum install -y ceph-common

[any node] $ sudo install -m 0644 ceph.conf /etc/ceph/ceph.conf
[any node] $ sudo install -m 0600 ceph.keyring /etc/ceph/ceph.keyring

Adding hosts to the cluster

For each new host you’d like to add to the cluster, you need to do two things:

  1. Install the cluster’s public SSH key in the new host’s root user’s authorized_keys file. For example,:

    [monitor 1] # cat | ssh root@*newhost* tee -a /root/.ssh/authorized_keys
  2. Tell Ceph that the new node is part of the cluster:

    [monitor 1] # ceph orch host add *newhost*

Deploying additional monitors

Normally a Ceph cluster has at least three (or, preferably, five) monitor daemons spread across different hosts. Since we are deploying a monitor, we again need to specify what IP address it will use, either as a simple IP address or as a CIDR network name.

To deploy additional monitors,:

[monitor 1] # ceph orch apply mon *<new-num-monitors>* *<host1:network1> [<host1:network2>...]*

For example, to deploy a second monitor on newhost using an IP address in network,:

[monitor 1] # ceph orch apply mon 2 newhost:

Deploying OSDs

To add an OSD to the cluster, you need to know the device name for the block device (hard disk or SSD) that will be used. Then,:

[monitor 1] # ceph orch osd create *<host>*:*<path-to-device>*

For example, to deploy an OSD on host newhost’s SSD,:

[monitor 1] # ceph orch osd create newhost:/dev/disk/by-id/ata-WDC_WDS200T2B0A-00SM50_182294800028

Deploying manager daemons

It is a good idea to have at least one backup manager daemon. To deploy one or more new manager daemons,:

[monitor 1] # ceph orch apply mgr *<new-num-mgrs>* [*<host1>* ...]

Deploying MDSs

In order to use the CephFS file system, one or more MDS daemons is needed.