Configuring the iSCSI Target using Ansible

The Ceph iSCSI gateway is the iSCSI target node and also a Ceph client node. The Ceph iSCSI gateway can be a standalone node or be colocated on a Ceph Object Store Disk (OSD) node. Completing the following steps will install, and configure the Ceph iSCSI gateway for basic operation.

Requirements:

  • A running Ceph Luminous (12.2.x) cluster or newer
  • RHEL/CentOS 7.5; Linux kernel v4.16 or newer; or the Ceph iSCSI client test kernel
  • The ceph-iscsi-config package installed on all the iSCSI gateway nodes

Installing:

  1. On the Ansible installer node, which could be either the administration node or a dedicated deployment node, perform the following steps:

    1. As root, install the ceph-ansible package:

      # yum install ceph-ansible
      
    2. Add an entry in /etc/ansible/hosts file for the gateway group:

      [ceph-iscsi-gw]
      ceph-igw-1
      ceph-igw-2
      

Note

If co-locating the iSCSI gateway with an OSD node, then add the OSD node to the [ceph-iscsi-gw] section.

Configuring:

The ceph-ansible package places a file in the /usr/share/ceph-ansible/group_vars/ directory called ceph-iscsi-gw.sample. Create a copy of this sample file named ceph-iscsi-gw.yml. Review the following Ansible variables and descriptions, and update accordingly.

Variable Meaning/Purpose
seed_monitor Each gateway needs access to the ceph cluster for rados and rbd calls. This means the iSCSI gateway must have an appropriate /etc/ceph/ directory defined. The seed_monitor host is used to populate the iSCSI gateway’s /etc/ceph/ directory.
cluster_name Define a custom storage cluster name.
gateway_keyring Define a custom keyring name.
deploy_settings If set to true, then deploy the settings when the playbook is ran.
perform_system_checks This is a boolean value that checks for multipath and lvm configuration settings on each gateway. It must be set to true for at least the first run to ensure multipathd and lvm are configured properly.
gateway_iqn This is the iSCSI IQN that all the gateways will expose to clients. This means each client will see the gateway group as a single subsystem.
gateway_ip_list The ip list defines the IP addresses that will be used on the front end network for iSCSI traffic. This IP will be bound to the active target portal group on each node, and is the access point for iSCSI traffic. Each IP should correspond to an IP available on the hosts defined in the ceph-iscsi-gw host group in /etc/ansible/hosts.
rbd_devices This section defines the RBD images that will be controlled and managed within the iSCSI gateway configuration. Parameters like pool and image are self explanatory. Here are the other parameters: size = This defines the size of the RBD. You may increase the size later, by simply changing this value, but shrinking the size of an RBD is not supported and is ignored. host = This is the iSCSI gateway host name that will be responsible for the rbd allocation/resize. Every defined rbd_device entry must have a host assigned. state = This is typical Ansible syntax for whether the resource should be defined or removed. A request with a state of absent will first be checked to ensure the rbd is not mapped to any client. If the RBD is unallocated, it will be removed from the iSCSI gateway and deleted from the configuration.
client_connections This section defines the iSCSI client connection details together with the LUN (RBD image) masking. Currently only CHAP is supported as an authentication mechanism. Each connection defines an image_list which is a comma separated list of the form pool.rbd_image[,pool.rbd_image]. RBD images can be added and removed from this list, to change the client masking. Note that there are no checks done to limit RBD sharing across client connections.

Note

When using the gateway_iqn variable, and for Red Hat Enterprise Linux clients, installing the iscsi-initiator-utils package is required for retrieving the gateway’s IQN name. The iSCSI initiator name is located in the /etc/iscsi/initiatorname.iscsi file.

Deploying:

On the Ansible installer node, perform the following steps.

  1. As root, execute the Ansible playbook:

    # cd /usr/share/ceph-ansible
    # ansible-playbook ceph-iscsi-gw.yml
    

    Note

    The Ansible playbook will handle RPM dependencies, RBD creation and Linux IO configuration.

  2. Verify the configuration from an iSCSI gateway node:

    # gwcli ls
    

    Note

    For more information on using the gwcli command to install and configure a Ceph iSCSI gateaway, see the Configuring the iSCSI Target using the Command Line Interface section.

    Important

    Attempting to use the targetcli tool to change the configuration will result in the following issues, such as ALUA misconfiguration and path failover problems. There is the potential to corrupt data, to have mismatched configuration across iSCSI gateways, and to have mismatched WWN information, which will lead to client multipath problems.

Service Management:

The ceph-iscsi-config package installs the configuration management logic and a Systemd service called rbd-target-gw. When the Systemd service is enabled, the rbd-target-gw will start at boot time and will restore the Linux IO state. The Ansible playbook disables the target service during the deployment. Below are the outcomes of when interacting with the rbd-target-gw Systemd service.

# systemctl <start|stop|restart|reload> rbd-target-gw
  • reload

    A reload request will force rbd-target-gw to reread the configuration and apply it to the current running environment. This is normally not required, since changes are deployed in parallel from Ansible to all iSCSI gateway nodes

  • stop

    A stop request will close the gateway’s portal interfaces, dropping connections to clients and wipe the current LIO configuration from the kernel. This returns the iSCSI gateway to a clean state. When clients are disconnected, active I/O is rescheduled to the other iSCSI gateways by the client side multipathing layer.

Administration:

Within the /usr/share/ceph-ansible/group_vars/ceph-iscsi-gw file there are a number of operational workflows that the Ansible playbook supports.

Warning

Before removing RBD images from the iSCSI gateway configuration, follow the standard procedures for removing a storage device from the operating system.

I want to…​ Update the ceph-iscsi-gw file by…​
Add more RBD images Adding another entry to the rbd_devices section with the new image.
Resize an existing RBD image Updating the size parameter within the rbd_devices section. Client side actions are required to pick up the new size of the disk.
Add a client Adding an entry to the client_connections section.
Add another RBD to a client Adding the relevant RBD pool.image name to the image_list variable for the client.
Remove an RBD from a client Removing the RBD pool.image name from the clients image_list variable.
Remove an RBD from the system Changing the RBD entry state variable to absent. The RBD image must be unallocated from the operating system first for this to succeed.
Change the clients CHAP credentials Updating the relevant CHAP details in client_connections. This will need to be coordinated with the clients. For example, the client issues an iSCSI logout, the credentials are changed by the Ansible playbook, the credentials are changed at the client, then the client performs an iSCSI login.
Remove a client Updating the relevant client_connections item with a state of absent. Once the Ansible playbook is ran, the client will be purged from the system, but the disks will remain defined to Linux IO for potential reuse.

Once a change has been made, rerun the Ansible playbook to apply the change across the iSCSI gateway nodes.

# ansible-playbook ceph-iscsi-gw.yml

Removing the Configuration:

The ceph-ansible package provides an Ansible playbook to remove the iSCSI gateway configuration and related RBD images. The Ansible playbook is /usr/share/ceph-ansible/purge_gateways.yml. When this Ansible playbook is ran a prompted for the type of purge to perform:

lio :

In this mode the LIO configuration is purged on all iSCSI gateways that are defined. Disks that were created are left untouched within the Ceph storage cluster.

all :

When all is chosen, the LIO configuration is removed together with all RBD images that were defined within the iSCSI gateway environment, other unrelated RBD images will not be removed. Ensure the correct mode is chosen, this operation will delete data.

Warning

A purge operation is destructive action against your iSCSI gateway environment.

Warning

A purge operation will fail, if RBD images have snapshots or clones and are exported through the Ceph iSCSI gateway.

[root@rh7-iscsi-client ceph-ansible]# ansible-playbook purge_gateways.yml
Which configuration elements should be purged? (all, lio or abort) [abort]: all


PLAY [Confirm removal of the iSCSI gateway configuration] *********************


GATHERING FACTS ***************************************************************
ok: [localhost]


TASK: [Exit playbook if user aborted the purge] *******************************
skipping: [localhost]


TASK: [set_fact ] *************************************************************
ok: [localhost]


PLAY [Removing the gateway configuration] *************************************


GATHERING FACTS ***************************************************************
ok: [ceph-igw-1]
ok: [ceph-igw-2]


TASK: [igw_purge | purging the gateway configuration] *************************
changed: [ceph-igw-1]
changed: [ceph-igw-2]


TASK: [igw_purge | deleting configured rbd devices] ***************************
changed: [ceph-igw-1]
changed: [ceph-igw-2]


PLAY RECAP ********************************************************************
ceph-igw-1                 : ok=3    changed=2    unreachable=0    failed=0
ceph-igw-2                 : ok=3    changed=2    unreachable=0    failed=0
localhost                  : ok=2    changed=0    unreachable=0    failed=0