Ceph in Kolla

Ceph in Kolla

The out-of-the-box Ceph deployment requires 3 hosts with at least one block device on each host that can be dedicated for sole use by Ceph. However, with tweaks to the Ceph cluster you can deploy a healthy cluster with a single host and a single block device.

Requirements

  • A minimum of 3 hosts for a vanilla deploy
  • A minimum of 1 block device per host

Preparation

To prepare a disk for use as a Ceph OSD you must add a special partition label to the disk. This partition label is how Kolla detects the disks to format and bootstrap. Any disk with a matching partition label will be reformatted so use caution.

To prepare an OSD as a storage drive, execute the following operations:

Warning

ALL DATA ON $DISK will be LOST! Where $DISK is /dev/sdb or something similar.

parted $DISK -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_BOOTSTRAP 1 -1

The following shows an example of using parted to configure /dev/sdb for usage with Kolla.

parted /dev/sdb -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_BOOTSTRAP 1 -1
parted /dev/sdb print
Model: VMware, VMware Virtual S (scsi)
Disk /dev/sdb: 10.7GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number  Start   End     Size    File system  Name                      Flags
     1      1049kB  10.7GB  10.7GB               KOLLA_CEPH_OSD_BOOTSTRAP

Using an external journal drive

The steps documented above created a journal partition of 5 GByte and a data partition with the remaining storage capacity on the same tagged drive.

It is a common practice to place the journal of an OSD on a separate journal drive. This section documents how to use an external journal drive.

Prepare the storage drive in the same way as documented above:

Warning

ALL DATA ON $DISK will be LOST! Where $DISK is /dev/sdb or something similar.

parted $DISK -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_BOOTSTRAP_FOO 1 -1

To prepare the journal external drive execute the following command:

parted $DISK -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_BOOTSTRAP_FOO_J 1 -1

Note

Use different suffixes (_42, _FOO, _FOO42, ..) to use different external journal drives for different storage drives. One external journal drive can only be used for one storage drive.

Note

The partition labels KOLLA_CEPH_OSD_BOOTSTRAP and KOLLA_CEPH_OSD_BOOTSTRAP_J are not working when using external journal drives. It is required to use suffixes (_42, _FOO, _FOO42, ..). If you want to setup only one storage drive with one external journal drive it is also necessary to use a suffix.

Configuration

Edit the [storage] group in the inventory which contains the hostname of the hosts that have the block devices you have prepped as shown above.

[storage]
controller
compute1

Enable Ceph in /etc/kolla/globals.yml:

enable_ceph: "yes"

RadosGW is optional, enable it in /etc/kolla/globals.yml:

enable_ceph_rgw: "yes"

Note

Regarding number of placement groups (PGs)

Kolla sets very conservative values for the number of PGs per pool (ceph_pool_pg_num and ceph_pool_pgp_num). This is in order to ensure the majority of users will be able to deploy Ceph out of the box. It is highly recommended to consult the official Ceph documentation regarding these values before running Ceph in any kind of production scenario.

RGW requires a healthy cluster in order to be successfully deployed. On initial start up, RGW will create several pools. The first pool should be in an operational state to proceed with the second one, and so on. So, in the case of an all-in-one deployment, it is necessary to change the default number of copies for the pools before deployment. Modify the file /etc/kolla/config/ceph.conf and add the contents:

[global]
osd pool default size = 1
osd pool default min size = 1

To build a high performance and secure Ceph Storage Cluster, the Ceph community recommend the use of two separate networks: public network and cluster network. Edit the /etc/kolla/globals.yml and configure the cluster_interface:

cluster_interface: "eth2"

For more details, see NETWORK CONFIGURATION REFERENCE of Ceph Documentation.

Deployment

Finally deploy the Ceph-enabled OpenStack:

kolla-ansible deploy -i path/to/inventory

Using a Cache Tiering

An optional cache tiering can be deployed by formatting at least one cache device and enabling cache. tiering in the globals.yml configuration file.

To prepare an OSD as a cache device, execute the following operations:

parted $DISK -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_CACHE_BOOTSTRAP 1 -1

Enable the Ceph cache tier in /etc/kolla/globals.yml:

enable_ceph: "yes"
ceph_enable_cache: "yes"
# Valid options are [ forward, none, writeback ]
ceph_cache_mode: "writeback"

After this run the playbooks as you normally would, for example:

kolla-ansible deploy -i path/to/inventory

Setting up an Erasure Coded Pool

Erasure code is the new big thing from Ceph. Kolla has the ability to setup your Ceph pools as erasure coded pools. Due to technical limitations with Ceph, using erasure coded pools as OpenStack uses them requires a cache tier. Additionally, you must make the choice to use an erasure coded pool or a replicated pool (the default) when you initially deploy. You cannot change this without completely removing the pool and recreating it.

To enable erasure coded pools add the following options to your /etc/kolla/globals.yml configuration file:

# A requirement for using the erasure-coded pools is you must setup a cache tier
# Valid options are [ erasure, replicated ]
ceph_pool_type: "erasure"
# Optionally, you can change the profile
#ceph_erasure_profile: "k=4 m=2 ruleset-failure-domain=host"

Managing Ceph

Check the Ceph status for more diagnostic information. The sample output below indicates a healthy cluster:

docker exec ceph_mon ceph -s

cluster:
  id:     f2ed6c00-c043-4e1c-81b6-07c512db26b1
  health: HEALTH_OK

services:
  mon: 1 daemons, quorum 172.16.31.121
  mgr: poc12-01(active)
  osd: 4 osds: 4 up, 4 in; 5 remapped pgs

data:
  pools:   4 pools, 512 pgs
  objects: 0 objects, 0 bytes
  usage:   432 MB used, 60963 MB / 61395 MB avail
  pgs:     512 active+clean

If Ceph is run in an all-in-one deployment or with less than three storage nodes, further configuration is required. It is necessary to change the default number of copies for the pool. The following example demonstrates how to change the number of copies for the pool to 1:

docker exec ceph_mon ceph osd pool set rbd size 1

All the pools must be modified if Glance, Nova, and Cinder have been deployed. An example of modifying the pools to have 2 copies:

for p in images vms volumes backups; do docker exec ceph_mon ceph osd pool set ${p} size 2; done

If using a cache tier, these changes must be made as well:

for p in images vms volumes backups; do docker exec ceph_mon ceph osd pool set ${p}-cache size 2; done

The default pool Ceph creates is named rbd. It is safe to remove this pool:

docker exec ceph_mon ceph osd pool delete rbd rbd --yes-i-really-really-mean-it

Troubleshooting

Deploy fails with ‘Fetching Ceph keyrings … No JSON object could be decoded’

If an initial deploy of Ceph fails, perhaps due to improper configuration or similar, the cluster will be partially formed and will need to be reset for a successful deploy.

In order to do this the operator should remove the ceph_mon_config volume from each Ceph monitor node:

ansible -i ansible/inventory/multinode \
    -a 'docker volume rm ceph_mon_config' \
    ceph-mon

Simple 3 Node Example

This example will show how to deploy Ceph in a very simple setup using 3 storage nodes. 2 of those nodes (kolla1 and kolla2) will also provide other services like control, network, compute, and monitoring. The 3rd (kolla3) node will only act as a storage node.

This example will only focus on the Ceph aspect of the deployment and assumes that you can already deploy a fully functional environment using 2 nodes that does not employ Ceph yet. So we will be adding to the existing multinode inventory file you already have.

Each of the 3 nodes are assumed to have two disk, /dev/sda (40GB) and /dev/sdb (10GB). Size is not all that important… but for now make sure each sdb disk are of the same size and are at least 10GB. This example will use a single disk (/dev/sdb) for both Ceph data and journal. It will not implement caching.

Here is the top part of the multinode inventory file used in the example environment before adding the 3rd node for Ceph:

[control]
# These hostname must be resolvable from your deployment host
kolla1.ducourrier.com
kolla2.ducourrier.com

[network]
kolla1.ducourrier.com
kolla2.ducourrier.com

[compute]
kolla1.ducourrier.com
kolla2.ducourrier.com

[monitoring]
kolla1.ducourrier.com
kolla2.ducourrier.com

[storage]
kolla1.ducourrier.com
kolla2.ducourrier.com

Configuration

To prepare the 2nd disk (/dev/sdb) of each nodes for use by Ceph you will need to add a partition label to it as shown below:

parted /dev/sdb -s -- mklabel gpt mkpart KOLLA_CEPH_OSD_BOOTSTRAP 1 -1

Make sure to run this command on each of the 3 nodes or the deployment will fail.

Next, edit the multinode inventory file and make sure the 3 nodes are listed under [storage]. In this example I will add kolla3.ducourrier.com to the existing inventory file:

[control]
# These hostname must be resolvable from your deployment host
kolla1.ducourrier.com
kolla2.ducourrier.com

[network]
kolla1.ducourrier.com
kolla2.ducourrier.com

[compute]
kolla1.ducourrier.com
kolla2.ducourrier.com

[monitoring]
kolla1.ducourrier.com
kolla2.ducourrier.com

[storage]
kolla1.ducourrier.com
kolla2.ducourrier.com
kolla3.ducourrier.com

It is now time to enable Ceph in the environment by editing the /etc/kolla/globals.yml file:

enable_ceph: "yes"
enable_ceph_rgw: "yes"
enable_cinder: "yes"
glance_backend_file: "no"
glance_backend_ceph: "yes"

Deployment

Finally deploy the Ceph-enabled configuration:

kolla-ansible deploy -i path/to/inventory-file
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