This document is for a development version of Ceph.
To list hosts associated with the cluster:
ceph orch host ls [--format yaml]
Hosts must have these Requirements installed. Hosts without all the necessary requirements will fail to be added to the cluster.
To add each new host to the cluster, perform two steps:
Install the cluster’s public SSH key in the new host’s root user’s
ssh-copy-id -f -i /etc/ceph/ceph.pub root@*<new-host>*
ssh-copy-id -f -i /etc/ceph/ceph.pub root@host2 ssh-copy-id -f -i /etc/ceph/ceph.pub root@host3
Tell Ceph that the new node is part of the cluster:
ceph orch host add *newhost*
ceph orch host add host2 ceph orch host add host3
If the node that want you to remove is running OSDs, make sure you remove the OSDs from the node.
To remove a host from a cluster, do the following:
For all Ceph service types, except for
the host from the placement specification file (for example, cluster.yml).
For example, if you are removing the host named host2, remove all occurrences of
- host2 from all
service_type: rgw placement: hosts: - host1 - host2
service_type: rgw placement: hosts: - host1
Remove the host from cephadm’s environment:
ceph orch host rm host2
If the host is running
node-exporter and crash services, remove them by running
the following command on the host:
cephadm rm-daemon --fsid CLUSTER_ID --name SERVICE_NAME
The orchestrator supports assigning labels to hosts. Labels are free form and have no particular meaning by itself and each host can have multiple labels. They can be used to specify placement of daemons. See Placement by labels
Labels can be added when adding a host with the
ceph orch host add my_hostname --labels=my_label1 ceph orch host add my_hostname --labels=my_label1,my_label2
To add a label a existing host, run:
ceph orch host label add my_hostname my_label
To remove a label, run:
ceph orch host label rm my_hostname my_label
Place a host in and out of maintenance mode (stops all Ceph daemons on host):
ceph orch host maintenance enter <hostname> [--force] ceph orch host maintenace exit <hostname>
Where the force flag when entering maintenance allows the user to bypass warnings (but not alerts)
Many hosts can be added at once using
ceph orch apply -i by submitting a multi-document YAML file:
--- service_type: host addr: node-00 hostname: node-00 labels: - example1 - example2 --- service_type: host addr: node-01 hostname: node-01 labels: - grafana --- service_type: host addr: node-02 hostname: node-02
This can be combined with service specifications (below) to create a cluster spec
file to deploy a whole cluster in one command. see
cephadm bootstrap --apply-spec
also to do this during bootstrap. Cluster SSH Keys must be copied to hosts prior to adding them.
Cephadm uses SSH to connect to remote hosts. SSH uses a key to authenticate with those hosts in a secure way.
Cephadm stores an SSH key in the monitor that is used to connect to remote hosts. When the cluster is bootstrapped, this SSH key is generated automatically and no additional configuration is necessary.
A new SSH key can be generated with:
ceph cephadm generate-key
The public portion of the SSH key can be retrieved with:
ceph cephadm get-pub-key
The currently stored SSH key can be deleted with:
ceph cephadm clear-key
You can make use of an existing key by directly importing it with:
ceph config-key set mgr/cephadm/ssh_identity_key -i <key> ceph config-key set mgr/cephadm/ssh_identity_pub -i <pub>
You will then need to restart the mgr daemon to reload the configuration with:
ceph mgr fail
Configuring a different SSH user¶
Cephadm must be able to log into all the Ceph cluster nodes as an user that has enough privileges to download container images, start containers and execute commands without prompting for a password. If you do not want to use the “root” user (default option in cephadm), you must provide cephadm the name of the user that is going to be used to perform all the cephadm operations. Use the command:
ceph cephadm set-user <user>
Prior to running this the cluster ssh key needs to be added to this users authorized_keys file and non-root users must have passwordless sudo access.
Customizing the SSH configuration¶
Cephadm generates an appropriate
ssh_config file that is
used for connecting to remote hosts. This configuration looks
something like this:
Host * User root StrictHostKeyChecking no UserKnownHostsFile /dev/null
There are two ways to customize this configuration for your environment:
Import a customized configuration file that will be stored by the monitor with:
ceph cephadm set-ssh-config -i <ssh_config_file>
To remove a customized SSH config and revert back to the default behavior:
ceph cephadm clear-ssh-config
You can configure a file location for the SSH configuration file with:
ceph config set mgr mgr/cephadm/ssh_config_file <path>
We do not recommend this approach. The path name must be visible to any mgr daemon, and cephadm runs all daemons as containers. That means that the file either need to be placed inside a customized container image for your deployment, or manually distributed to the mgr data directory (
/var/lib/ceph/<cluster-fsid>/mgr.<id>on the host, visible at
/var/lib/ceph/mgr/ceph-<id>from inside the container).
Fully qualified domain names vs bare host names¶
cephadm has very minimal requirements when it comes to resolving host names etc. When cephadm initiates an ssh connection to a remote host, the host name can be resolved in four different ways:
a custom ssh config resolving the name to an IP
via an externally maintained
via explicitly providing an IP address to cephadm:
ceph orch host add <hostname> <IP>
automatic name resolution via DNS.
Ceph itself uses the command
hostname to determine the name of the
cephadm demands that the name of the host given via
ceph orch host add
equals the output of
hostname on remote hosts.
Otherwise cephadm can’t be sure, the host names returned by
ceph * metadata match the hosts known to cephadm. This might result
in a CEPHADM_STRAY_HOST warning.
When configuring new hosts, there are two valid ways to set the
hostname of a host:
Using the bare host name. In this case:
hostnamereturns the bare host name.
hostname -freturns the FQDN.
Using the fully qualified domain name as the host name. In this case:
hostnamereturns the FQDN
hostname -sreturn the bare host name
man hostname recommends
hostname to return the bare
The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver(3) returns for the host name, such as, ursula.example.com. It is usually the hostname followed by the DNS domain name (the part after the first dot). You can check the FQDN using
hostname --fqdnor the domain name using
dnsdomainname.You cannot change the FQDN with hostname or dnsdomainname. The recommended method of setting the FQDN is to make the hostname be an alias for the fully qualified name using /etc/hosts, DNS, or NIS. For example, if the hostname was "ursula", one might have a line in /etc/hosts which reads 127.0.1.1 ursula.example.com ursula
man hostname recommends
hostname to return the bare
host name. This in turn means that Ceph will return the bare host names
ceph * metadata. This in turn means cephadm also
requires the bare host name when adding a host to the cluster:
ceph orch host add <bare-name>.