Using host labels to deploy daemons on specific hosts

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You can use host labels to deploy daemons to specific hosts. There are two ways to use host labels to deploy daemons on specific hosts:

By using the --placement option from the command line.
By using a YAML file.

Prerequisites

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A storage cluster that has been installed and bootstrapped.
Root-level access to all nodes in the storage cluster.

Procedure

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Log into the Cephadm shell:

Example
```
[root@host01 ~]# cephadm shell
```

List current hosts and labels:

Example

[ceph: root@host01 /]# ceph orch host ls

HOST      ADDR     LABELS               STATUS
host01              _admin,mon,osd,mgr
host02              mon,osd,mgr,mylabel

Method 1: Use the --placement option to deploy a daemon from the command line:

Syntax

ceph orch apply DAEMON --placement="label:LABEL"

Example

[ceph: root@host01 /]# ceph orch apply prometheus --placement="label:mylabel"

Method 2: To assign the daemon to a specific host label in a YAML file, specify the service type and label in the YAML file:
1. Create the placement.yml file:
  
  Example
```
[ceph: root@host01 /]# vi placement.yml
```
2. Specify the service type and label in the placement.yml file:
  
  Example
```
service_type: prometheus
placement:
  label: "mylabel"
```
3. Apply the daemon placement file:
  
  Syntax
```
ceph orch apply -i FILENAME
```
  Example
```
[ceph: root@host01 /]# ceph orch apply -i placement.yml
Scheduled prometheus update…
```

Verification

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List the status of the daemons:

Syntax

ceph orch ps --daemon_type=DAEMON_NAME

Example

[ceph: root@host01 /]# ceph orch ps --daemon_type=prometheus
NAME               HOST   PORTS   STATUS        REFRESHED  AGE  MEM USE  MEM LIM  VERSION  IMAGE ID      CONTAINER ID
prometheus.host02  host02  *:9095  running (2h)     8m ago   2h    85.3M        -  2.22.2   ac25aac5d567  ad8c7593d7c0