Linux cluster

Red Hat High-Availability Add-on Overview

Shared storage might be a SAN-attached device, Fibre channel attached device, or TCP/IP attached device. The device might be attached to all nodes simultaneously, or cluster resource manager can attach it to the active node only. The device might be in turn a resilient one, presenting the distributed file system with software or hardware replication between filesystem nodes. In the case of a geographically distributed cluster, the shared storage also can be distributed geographically in the same way as cluster nodes, and cluster resource manager can attach to the node the storage instance in the same geo location.

The possible configurable options are:

• For a shared physical device
• For a shared operational system (Gluster FS)
• FIXEdge Logs Replicator
• DRBD

Shared physical device

To service multiple FIX sessions reliably FIXEdge can be deployed in Linux HA cluster with 2 or 3 nodes and shared storage. Cluster solution utilizes Corosync and Pacemaker – tools that facilitate HA Linux cluster for applications that do not have native support for clustering. Health checks are used to figure out if a node or an application that runs on the node is operating properly.  Node health checks are implemented by monitoring FE PID file. 

Two or three nodes constitute a cluster and at any moment only one of them runs FE (active-passive cluster). When a failure of active FE node is detected shared FIX message file system storage is unmounted on that node and mounted on the second node, then FE is started on the second node. All sessions are handled by the one active server and will be started on another node in case of failure. This approach leaves no opportunity to balance the load between the cluster nodes. FIXEdge start-up time grows with the number of the session it serves. 

Multiple FIXEdge nodes need to have a consistent view of the FIX sessions' state, which includes the messages and sequence numbers. Multiple approaches are possible to provide such a view. The simplest is to use a shared network filesystem (e.g. NFS share), the drawbacks are significantly increased latency (approx 20 times slower). The recommended configuration is to use a SAN storage attach simultaneously to all cluster nodes. The storage itself is a block device that is mounted on the node where the FIXEdge is currently run. This approach allows having shared storage for all nodes while keeping I/O latency low.

To access the FIXEdge running on the cluster the virtual IP is configured on the node where FIXEdge runs. All FIX client and the FIXICC administration tool connect to the active node via virtual IP.

This approach gives a working highly-available solution and works well for active-passive clusters with few nodes and static FIX session configuration.

Environment Requirements

1. Network:
   1. The channel between FE and data provider - max wide
   2. dedicated network for cluster synchronization (heartbeats)
2. Open ports:
   1. high-availability service
   2. 8005/tcp
   3. 8901/tcp
   4. 8905/tcp
   5. 1234/udp
3. Application: 
   1. 1 Core per 1 Data Provider (recommended for latency)
   2. 1G for binaries
   3. Collocated nodes in one DC for max performance
   4. Health-check interval sufficient for FIXEdge to start
4. Storage:
   1. Mandatory Fibre Channel SAN storage for session logs - 1.5 TB, directly attached to both nodes. Encrypted via standard LVM features.
   2. Mandatory STONITH to ensure that FC storage is mounted on a single node
   3. Mandatory Archive for session logs - https://kb.b2bits.com/display/B2BITS/FIXEdge+Capacity 
   4. Shared storage (NFS/SMB) for configuration - can be slow.
5. Experimental features:
   1. Start/stop from FIXICC - concept conflicts with cluster control.
6. Operating system: RHEL 7 or newer.

Deployment Diagram

Scheduled Tasks

• Start FIXEdge at start-of-day - via pacemaker per FE resource by enabling resources (fixegde).
• Stop FIXEdge at end-of-day, for maintenance hours - via pacemaker by disabling resources (fixegde).
• Log archiving - mandatory for FIXEdge operation, FIXEdge needs available space on /opt/fixedge/FIXEdge1/log directory, so a periodic archiving of the files and directory cleanup is required.

Filesystem Layout

How to Deploy

Install cluster software

Instructions below should be run on each cluster node. Superuser privileges are required for all the steps.

1. Install packages from a repository:
   yum install corosync pcs pacemaker 
2. Set the password for the hacluster  user:
   passwd hacluster 
3. Open ports on the firewall:
   firewall-cmd --add-service=high-availability 
firewall-cmd --runtime-to-permanent 

4. Enable cluster services to run at the system start-up:
   systemctl enable pcsd corosync pacemaker 

Install FIXEdge

To install FIXEdge you first need four artifacts: the FIXEdge package (fixedge.tar.gz), the FIXEdge systemd  integration configuration (fixedge-systemd.tar.gz) and the license (engine.license). Superuser privileges are required for all the steps.

1. Install FIXEdge RPM package:
   mkdir --parents /opt/fixedge
tar --extract --file fixedge.tar.gz --directory /opt/fixedge 
2. Unpack the FIXEdge systemd integration configuration:
   tar --extract --file fixedge-systemd.tar.gz --directory /
3. Add a user and a group for the FIXEdge:
   groupadd --system fixedge 
useradd --system --gid fixedge --home-dir /opt/fixedge --shell /sbin/nologin --comment "Account to own and run FIXEdge" fixedge 
4. Change ownership of the FIXEdge to the dedicated user:
   chown --recursive fixedge:fixedge /opt/fixedge 
5. Copy the license:
   cp engine.license /opt/fixedge 
6. Enable FIXICC Agent to start at the system start-up:
   systemctl enable fixicc-agent 

Firewall Configuration

1. Open ports for FIXEdge on the firewall:
   firewall-cmd --add-port=8005/tcp --add-port=8901/tcp --add-port=8903/tcp --add-port=8905/tcp --add-port=1234/udp 
firewall-cmd --runtime-to-permanent

Prepare Storage for the Session Logs and the Configuration

At this point FIXEdge is deployed locally, now we need to make the configuration and the state shared.

1. Make an NFS share, copy files from /opt/fixedge/FIXEdge1/conf to the share and mount it to /opt/fixedge/FIXEdge1/conf .

Use a Dual-Port SAN Device

1. Create an LVM volume group for the shared session logs storage:
   vgcreate shared_logs_group <SAN_STORAGE_DEVICE> 
   replace SAN_STORAGE_DEVICE with the actual device name of SAN storage.
2. Create a logical volume for the session logs:
   lvcreate shared_logs_group --extents 100%FREE --name shared_logs 

Prepare the logs storage, this commands must be executed on a single node.

1. Create a filesystem on the logical volume:
   mkfs -t xfs /dev/shared_logs_group/shared_logs 
2. Mount the filesystem:
   mount /dev/shared_logs_group/shared_logs /opt/fixedge/FIXEdge1/log 
3. Create FIXEdge log directory structure:
   mkdir /opt/fixedge/FIXEdge1/log/archive /opt/fixedge/FIXEdge1/log/backup 
4. Unmount and deactivate:
   umount /opt/fixedge/FIXEdge1/log
vgchange -a n shared_logs_group

Set up a FIXEdge Cluster

Now we need to set up cluster resources for the FIXEdge. Superuser privileges are required for all the steps.

1. Authorize nodes for hacluster  user:
   pcs cluster auth NODE_1_NAME NODE_2_NAME -u hacluster 

   Where NODE_1_NAME  and NODE_2_NAME are the hostnames of the servers which run FIXEdge. Note that these names must not resolve to 127.0.0.1 locally or use IP addresses instead of the hostnames.

2. Create the cluster and add nodes:
   pcs cluster setup --force --name fixedge_ha NODE_1_NAME NODE_2_NAME 
   Where NODE_1_NAME  and NODE_2_NAME are the hostnames of the servers which run FIXEdge. Note that these names must not resolve to 127.0.0.1 locally or use IP addresses instead of the hostnames.

3. Start cluster

   pcs cluster start --all 
   Now the cluster is starting up, you can check its status with commands:
   pcs status cluster 
pcs status nodes 
4. Disable resource migration on the first failure, since restarting on the same node takes less time than migration to another node:
   pcs property set start-failure-is-fatal=false 
5. For two-nodes cluster we must disable the quorum, do not do this for a three-node cluster. Quorum avoids the situation when cluster cannot decide which node is active.
   pcs property set no-quorum-policy=ignore 
6. Add a virtual IP as a resource to the cluster:
   pcs resource create virtual_ip ocf:heartbeat:IPaddr2 ip=<VIRTUAL_IP> cidr_netmask=32 op monitor interval=30s 
   where <VIRTUAL_IP> is the IP that will be used by the FIX clients to connect to the cluster.

Use a Dual-Port SAN Device

1. Add LVM group for the sessions' logs as a resource to the cluster:
   pcs resource create logs_vg ocf:heartbeat:LVM volgrpname=logs 
2. Add filesystem for the sessions' logs as a resource to the cluster:
   pcs resource create logs_fs ocf:heartbeat:Filesystem device=/dev/shared_logs_group/shared_logs directory=/opt/fixedge/FIXEdge1/log fstype=xfs 
3. Add FIXEdge as a resource to the cluster:
   pcs resource create fixedge systemd:fixedge op start timeout=300s op stop timeout=60s op monitor interval=10 timeout=60s meta migration-threshold=3 
4. Make sure that all resources are started on the same node:
   pcs constraint colocation set virtual_ip logs_vg logs_fs fixedge sequential=true setoptions score=INFINITY 
5. Make sure that resources are started in the proper order:
   pcs constraint order set virtual_ip logs_vg logs_fs fixedge 

How to Validate the Installation

Use FIXICC to connect to the cluster nodes: add servers with addresses of the cluster nodes. The FIXICC will show one server running and another stopped.

Use FIX Client Simulator to connect to FIXEdge via Virtual IP.

Cluster logs are located at /var/log/cluster .

FIXEdge logs are at /opt/fixedge/FIXEdge1/log/FixEdge.log , /opt/fixedge/fixicc-agent/logs/fixicc-agent.log , and /opt/fixedge/fixicc-agent/logs/wrapper.log

1. Search for FATAL and ERROR entries in the logs
2. Contact support (SupportFIXAntenna@epam.com) and provide the logs.

Open https://NODE_1_NAME:2224/ to access pacemaker's WebUI. It provides means for inspecting the state of the cluster nodes and resources. Under normal operation, all nodes and resources must be running. All resources must be running the same node.

Try stopping the active node (shut it down), the resources will be moved to another node.

Setting up GlusterFS Server 

In general, the cluster might look like this:

In this setup, the TCP/IP attached device is used. A two nodes GlusterFS file server with mirroring is used as the shared device. The device is mounted to both nodes simultaneously. See the diagram below:

Reference articles:

http://blog.bobbyallen.me/2013/01/26/creating-a-highly-available-file-server-cluster-for-a-web-farm-using-ubuntu-12-04-lts/

http://www.sohailriaz.com/glusterfs-howto-on-centos-6-x/

Install software

Do these steps on both servers: EVUAKYISD105A.kyiv.epam.com and EVUAKYISD105D.kyiv.epam.com

$ sudo wget -P /etc/yum.repos.d http://download.gluster.org/pub/gluster/glusterfs/LATEST/CentOS/glusterfs-epel.repo
$ sudo yum install glusterfs
$ sudo yum install glusterfs-fuse
$ sudo yum install glusterfs-server

$ glusterfsd --version

glusterfs 3.6.2 built on Jan 22 2015 12:58:10
Repository revision: git://git.gluster.com/glusterfs.git
Copyright (c) 2006-2013 Red Hat, Inc. <http://www.redhat.com/>
GlusterFS comes with ABSOLUTELY NO WARRANTY.
It is licensed to you under your choice of the GNU Lesser
General Public License, version 3 or any later version (LGPLv3
or later), or the GNU General Public License, version 2 (GPLv2),
in all cases as published by the Free Software Foundation.

$ sudo /etc/init.d/glusterd start
$ sudo chkconfig glusterfsd on

Configure

Do these steps only on one server. For example, on EVUAKYISD105A.kyiv.epam.com

$ sudo gluster peer probe EVUAKYISD105D.kyiv.epam.com

$ sudo gluster peer status
Number of Peers: 1
Hostname: EVUAKYISD105D.kyiv.epam.com
Uuid: 04126ea4-a0e5-4854-a38e-69c24d9c05aa
State: Peer in Cluster (Connected)

$ cd /
$ sudo mkdir data
$ sudo chmod a+rwx /data

$ sudo gluster volume create clusterdata replica 2 transport tcp EVUAKYISD105A.kyiv.epam.com:/data EVUAKYISD105D.kyiv.epam.com:/data force

volume create: clusterdata: success: please start the volume to access data
 
$ sudo gluster volume start clusterdata

volume start: clusterdata: success
 
$ sudo gluster volume info


Volume Name: clusterdata
Type: Replicate
Volume ID: fa31c2de-f7d6-4f05-97e5-e310d2680d94
Status: Started
Number of Bricks: 1 x 2 = 2
Transport-type: tcp
Bricks:
Brick1: EVUAKYISD105A.kyiv.epam.com:/data
Brick2: EVUAKYISD105D.kyiv.epam.com:/data

Mounting GlusterFS storage on FIXEdge cluster nodes

These commands shall be run on both FIXEdge nodes: EVUAKYISD103D.kyiv.epam.com and EVUAKYISD103C.kyiv.epam.com

$ sudo wget -P /etc/yum.repos.d http://download.gluster.org/pub/gluster/glusterfs/LATEST/CentOS/glusterfs-epel.repo
$ sudo yum install glusterfs-client

$ sudo mkdir /data
$ sudo chmod a+rwx /data
$ sudo mount.glusterfs EVUAKYISD105D.kyiv.epam.com:/clusterdata /data
 
$ mount
/dev/mapper/VolGroup00-LogVol00 on / type ext4 (rw,noatime,nodiratime,noacl,commit=60,errors=remount-ro)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
/dev/sda1 on /boot type ext4 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
EVUAKYISD105D.kyiv.epam.com:/clusterdata on /data type fuse.glusterfs (rw,default_permissions,allow_other,max_read=131072)

And now add the following line to /etc/fstab to ensure mounting after reboot:

       EVUAKYISD105A.kyiv.epam.com:/clusterdata        /data   glusterfs       defaults,_netdev        0 0

Setting up FIXEdge instances

Copy FixEdge-5.8.2.68334-Linux-2.6.32-gcc447-x86_64.tar.gz to /home/user to both nodes: EVUAKYISD103D.kyiv.epam.com and EVUAKYISD103C.kyiv.epam.com.

On the Node1

Unzip. Untar.

$ gunzip FixEdge-5.8.2.68334-Linux-2.6.32-gcc447-x86_64.tar.gz
$ tar xf FixEdge-5.8.2.68334-Linux-2.6.32-gcc447-x86_64.tar

Move installation folder to /home/user/FixEdge:

$ cd FixEdge
$ cd v.5.8.2.68334
$ mv * /home/user/FIXEdge
$ cd ..
$ rmdir v.5.8.2.68334

Upload licenses (engine.license and fixaj2-license.bin) to /home/user/FIXEdge folder.

Move FIXEdge instance folder to shared storage:

mv FixEdge1 /data/

Edit scripts in /home/user/FixEdge/bin to direct them to the new FIXEdge instance location:

• replace ".." with "/data".

Edit FIXICC Agent configuration:

• /home/user/FixEdge/fixicc-agent/conf/wrapper.conf
  • wrapper.daemon.pid.dir = ${wrapper_home}
• /home/user/FixEdge/fixicc-agent/conf/agent.properties 
  • EngineProperty = /data/FixEdge1/conf/engine.properties
  • FIXEdgeFileSettings = /data/FixEdge1/conf/FIXEdge.properties
  • LogUrl = /data/FixEdge1/log

Edit FIXEdge and engine configuration:

• /data/FixEdge1/conf/engine.properties 
  • EngineRoot = /data
  • LicenseFile = /home/user/FixEdge/engine.license
• /data/FixEdge1/conf/FIXEdge.properties
  
  • FIXEdge.RootDir = /data/FixEdge1
  • Log.File.RootDir = /data/FixEdge1
  • TransportLayer.SmtpTA.DllName = /home/user/FixEdge/bin/libSMTPTA.so

Install and Start FIXICC Agent daemon:

$ cd /home/user/FixEdge/fixicc-agent/bin
$ ./installDaemon.sh
$ ./startDaemon.sh

Now everything is ready to run FIXEdge on Node 1.

Prepare to copy the installation to Node 2:

$ cd /home/user
$ tar cvf FixEdge.tar FixEdge
$ gzip FixEdge.tar

Copy file FixEdge.tar.gz to Node2:/user/home

On the Node2

Unzip, untar

$ cd /home/user
$ gunzip FixEdge.tar.gz
$ tar xf FixEdge.tar

Install and Start FIXICC Agent daemon:

$ cd /home/user/FixEdge/fixicc-agent/bin
$ ./installDaemon.sh
$ ./startDaemon.sh

Open ports on both nodes

8005 for FIXICC Agent and 8901 for FIX Engine

$ sudo iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 8005 -j ACCEPT
$ sudo iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 8901 -j ACCEPT
$ sudo service iptables save

Configuring a failover cluster for FIXEdge with Pacemaker, Corosync & PCS

Reference articles:

http://jensd.be/?p=156

https://github.com/feist/pcs/issues/

On both nodes install needed software

$ sudo yum install corosync pcs pacemaker 

On both nodes set the password for hacluster user ('epmc-cmcc' was used)

$ sudo passwd hacluster

Configure Firewall on both nodes to allow cluster traffic:

$ sudo iptables -I INPUT -m state --state NEW -p udp -m multiport --dports 5404,5405 -j ACCEPT
$ sudo iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 2224 -j ACCEPT
$ sudo iptables -I INPUT -p igmp -j ACCEPT
$ sudo iptables -I INPUT -m addrtype --dst-type MULTICAST -j ACCEPT
$ sudo service iptables save

Start the pcsd service on both nodes

$ sudo systemctl start pcsd

From now on all commands needs to be executed on one node only. We can control the cluster by using PCS from on of the nodes.

Since we will configure all nodes from one point, we need to authenticate on all nodes before we are allowed to change the configuration. Use the previously configured hacluster user and password to do this:

$ sudo pcs cluster auth EVUAKYISD10AA.kyiv.epam.com EVUAKYISD10AB.kyiv.epam.com
Username: hacluster
Password:
EVUAKYISD10AA.kyiv.epam.com: Authorized
EVUAKYISD10AB.kyiv.epam.com: Authorized

Create the cluster and add nodes. This command command creates the cluster node configuration in /etc/corosync.conf.

$ sudo pcs cluster setup --name fixedge_cluster EVUAKYISD10AA.kyiv.epam.com EVUAKYISD10AB.kyiv.epam.com
Shutting down pacemaker/corosync services...
Redirecting to /bin/systemctl stop  pacemaker.service
Redirecting to /bin/systemctl stop  corosync.service
Killing any remaining services...
Removing all cluster configuration files...
EVUAKYISD10AA.kyiv.epam.com: Succeeded
EVUAKYISD10AB.kyiv.epam.com: Succeeded

We can start cluster now:

$ sudo pcs cluster start --all
EVUAKYISD10AB.kyiv.epam.com: Starting Cluster...
EVUAKYISD10AA.kyiv.epam.com: Starting Cluster...

We can check cluster status:

$ sudo pcs status cluster
Cluster Status:
 Last updated: Tue Jan 27 22:11:15 2015
 Last change: Tue Jan 27 22:10:48 2015 via crmd on EVUAKYISD10AA.kyiv.epam.com
 Stack: corosync
 Current DC: EVUAKYISD10AA.kyiv.epam.com (1) - partition with quorum
 Version: 1.1.10-32.el7_0.1-368c726
 2 Nodes configured
 0 Resources configured


$ sudo pcs status nodes
Pacemaker Nodes:
 Online: EVUAKYISD10AA.kyiv.epam.com EVUAKYISD10AB.kyiv.epam.com
 Standby:
 Offline:
 
$ sudo corosync-cmapctl | grep members
runtime.totem.pg.mrp.srp.members.1.config_version (u64) = 0
runtime.totem.pg.mrp.srp.members.1.ip (str) = r(0) ip(10.17.131.127)
runtime.totem.pg.mrp.srp.members.1.join_count (u32) = 1
runtime.totem.pg.mrp.srp.members.1.status (str) = joined
runtime.totem.pg.mrp.srp.members.2.config_version (u64) = 0
runtime.totem.pg.mrp.srp.members.2.ip (str) = r(0) ip(10.17.131.128)
runtime.totem.pg.mrp.srp.members.2.join_count (u32) = 1
runtime.totem.pg.mrp.srp.members.2.status (str) = joined


$ sudo pcs status corosync
Membership information
----------------------
    Nodeid      Votes Name
         1          1 EVUAKYISD10AA.kyiv.epam.com (local)
         2          1 EVUAKYISD10AB.kyiv.epam.com

Disable the STONITH option as we don't have STONITH devices in our demo virtual environment:

$ sudo pcs property set stonith-enabled=false

For two-nodes cluster we must disable the quorum:

$ sudo pcs property set no-quorum-policy=ignore
$ sudo pcs property
Cluster Properties:
 cluster-infrastructure: corosync
 dc-version: 1.1.10-32.el7_0.1-368c726
 no-quorum-policy: ignore
 stonith-enabled: false

Add Virtual IP as a resource to the cluster:

$ sudo pcs resource create virtual_ip ocf:heartbeat:IPaddr2 ip=10.17.135.17 cidr_netmask=32 op monitor interval=30s
$ sudo pcs status resources
 virtual_ip (ocf::heartbeat:IPaddr2): Started

Add FIXEdge as a resource to cluster:

$ sudo pcs resource create FIXEdge ocf:heartbeat:anything params binfile="/home/user/FixEdge/bin/FIXEdge" cmdline_options="/data/FixEdge1/conf/FIXEdge.properties" user="user" logfile="/home/user/FIXEdge_resource.log" errlogfile="/home/user/FIXEdge_resource_error.log"

$ sudo cp anything /usr/lib/ocf/resource.d/heartbeat/
$ sudo chmod a+rwx /usr/lib/ocf/resource.d/heartbeat/anything  

$ sudo visudo
Defaults    !requiretty
user    ALL=(user)      NOPASSWD: ALL
root    ALL=(user)      NOPASSWD: ALL

In order to make sure that the Virtual IP and FIXEdge always stay together, we can add a constraint:

$ sudo pcs constraint colocation add FIXEdge virtual_ip INFINITY

To avoid the situation where the FIXEdge would start before the virtual IP is started or owned by a certain node, we need to add another constraint which determines the order of availability of both resources:

$ sudo pcs constraint order virtual_ip then FIXEdge
Adding virtual_ip FIXEdge (kind: Mandatory) (Options: first-action=start then-action=start)

After configuring the cluster with the correct constraints, restart it and check the status:

$ sudo pcs cluster stop --all && sudo pcs cluster start --all
EVUAKYISD10AB.kyiv.epam.com: Stopping Cluster...
EVUAKYISD10AA.kyiv.epam.com: Stopping Cluster...
EVUAKYISD10AA.kyiv.epam.com: Starting Cluster...
EVUAKYISD10AB.kyiv.epam.com: Starting Cluster...

Cluster configuration is now completed.

Attachments

FIX Logs Replicator

FIX Antenna Replication tool (RT) is typically used for FIX session recovery on a backup FIX engine. It is deployed on the primary FIX engine (server - publisher) and backup destination(s) (subscriber- client). RT uses a custom transfer protocol to synchronize FIX logs between the primary and backups hosts in real time. It can be started at any time to resynchronize primary and backup FIX log files. It is highly optimized for high throughput to transfer data from multiple log files and to efficiently utilize bandwidth. RT comes with an Admin interface to operate and monitor the state of replication process.

FIXEdge Recovery Time Objective and Recovery Point Objective

The current article describes the Recovery Time Objective (RTO) and Recovery Point Objective(RPO) for Disaster recovery in case of active-passive Cluster configuration (see FIXEdge Failover Cluster installation).

Recovery Time Objective (RTO)

• Some functions are more important than others and may need a quicker recovery.
• The period of time within which systems, applications, or functions must be recovered after an outage is referred to as Recovery Time Objectives (RTOs).
• All business functions, applications or vendors that require a business continuity plan must have an RTO.

Recovery Point Objective(RPO)

• An RPO is the maximum allowable amount of data loss an organization can tolerate as a result of an event which causes systems recovery (the transfer of work) to an alternative system environment or location.
• An RPO is applicable only to applications that store data and are evaluated using similar to RTO requirements.

• The RPO is not the time it takes to restore data as part of recovery. The data restoration time is part of the RTO. 
  

Failover scenario #1. Application or cluster node failure

Failure of software or hardware within a node (e.g. application failure, node unavailability, resource exhausting). Failover Cluster consists of several application nodes. In case of one node fails – the application (or DB) is moved to another node and start there within approximately 2 minutes.

The session recovery procedure happens automatically. The missing messages should be recovered with a resend request procedure automatically.

Achievable RTO Values: "Greater than 0 seconds, up to and including 2 minutes"

Achievable RPO Values: "Recent synch point: Greater than 0 seconds, up to and including few seconds"

Failover scenario #2. Whole cluster failure

Disaster recovery environment should expect the connection. In case of disaster, the production environment is moved to DR. 

Achievable RTO Values: "Greater than 0 seconds, up to and including few seconds"

Achievable RPO Values: "Recent synch point: Greater than 0 seconds, up to and including 1 day, i.e. since the start of the day".