3 Active/Passive High Availability: Configuration planning

12.3.1 Network requirements

Because data is continually replicated between the two cluster nodes, carefully

consider your networking topology. Figure 12-5 shows a diagram of a typical

SDMC High Availability environment.

Note that the SDMC provides network path redundancy through two connections

to each Flexible Service Processor (FSP) of a managed system. When the front

and back IPs of the FSP are connected through different networks to the SDMC

and one of the networks goes down, then the connection is automatically

established to the FSP from the same SDMC through the other network,

providing continuous availability to the user.



Connected to 9.0.0.30



Active Node



Passive Node



IBM Systems Director

Management Console



IBM Systems Director

Management Console



eth09.0.0.11



eth09.0.0.21



eth110.0.0.11

Floating IP

eth0:1- 9.0.0.30



br0bridge



br1bridge



eth09.0.0.10



eth110.0.0.10



eth110.0.0.21



Virtual

machines



Hypervisor



br0bridge



br1bridge



eth09.0.0.20



eth110.0.0.20



Hardware



Public LAN

Private LAN



Figure 12-5 High Availability network topology



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Replication IP address

Because the replication IP address on each of the two SDMC nodes in the High

Availability cluster is used to constantly synchronize data, it is important that this

network connection be fast as possible.



Guidelines for the replication IP address

The guidelines for the replication IP address are:

If possible, use a separate private network for replication between the nodes

for better performance and place the two SDMCs within close range.

A high-speed Ethernet link, such as a crossover cable using gigabit Ethernet,

can be used to reduce latency for the initial and ongoing synchronization

between the active and passive SDMCs.



Network status IP address

Although having a network status IP address is optional, it is a best practice. The

nodes use this IP address to determine which node is connected to the network.

If they cannot contact each other, the node that can connect this IP address

becomes the active node.

If you do not specify a network status IP address, both nodes might become

active at the same time. If one node cannot connect to the other, it assumes that

the other node has lost network connectivity and makes itself the active node. If

both nodes have network connectivity but cannot connect to each other, both

nodes might become active.

If both nodes become active, changes might be made to both nodes, but all

changes made to one node are lost. When connectivity is restored, one node

becomes passive and the data on the active node is copied to it. Changes that

were made to the node that becomes the passive node are lost.



Guidelines for the network status IP address

The guidelines for the network status IP address are:

This address works best in domains where all nodes are in the same subnet.

Having the nodes in different subnets makes it more likely that both nodes

can ping the IP address, but they cannot communicate with each other.

Do not install a firewall rule that blocks ICMP traffic between the cluster nodes

and the network status IP instance.

Choose an address that the nodes can connect to only when they can

connect to the whole network.

Choose an address that is available most of the time.



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Choose an address that each node can reach by a single path. If there are

multiple paths, it is possible that one path is down, causing the ping to fail,

when the node is online.

Do not use an address that either node uses, including the floating IP

address.

The gateway address for the SDMC is a good candidate to use as a network

status IP address.



Floating IP address and agent manager IP address

The floating IP address is always initially assigned to the active node and is

reassigned to the secondary node that takes over as the active node during a

failure. This is the address that users should always access so that they always

connect to the currently active node.

If you use Common Agent Services (CAS) agents, they use the floating IP

address specified as the agent manager IP address to communicate with the

nodes. For information about common agents, see the Common Agent topic in

the Systems Director Information Center at:

http://publib.boulder.ibm.com/infocenter/director/v6r2x/index.jsp

The agent manager uses the agent manager IP address to identify itself to the

CAS agents that it manages. If you only specify one floating IP address, it is used

as the agent manager IP address. If you specify more than one floating IP

addresses, you can specify which one is the agent manager IP address.



Guidelines for the floating IP address

The guidelines for the floating IP address are:

It must not be in use.

All systems that need to connect to the nodes must be able to access this IP

address through your network.

If your nodes are connected to multiple networks, configure multiple floating

IP addresses.

All CAS agents you want to manage must be able to contact the floating IP

address that you specify as the Agent Manager address.



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12.3.2 DHCP considerations

The SDMC cannot be a DHCP client. If your network is set up so that one DHCP

server is running at a time (you have one range of DHCP addresses), then both

the SDMC network configurations must be identical and each network interface

card (NIC) must be connected to the same networks on each node. For example,

if eth0 is connected to the 192.168.1.0 network segment on the primary node,

then eth0 on the secondary node must also be connected to the same segment.

The SDMC High Availability environment can be configured in either a

non-shared or shared DHCP configuration, as shown in Figure 12-6 on

page 312.



Non-shared DHCP configuration

The DHCP server is run (and monitored) on each node. Configure each node to

use the same network interface (eth0 in Figure 12-6 on page 312) but to use

different address ranges.



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Shared DHCP configuration

The DHCP server is only run on the active node. Configure the first node as

using DHCP server with a specific address range. Choose the first reserved

address for the node. Configure the second node as a standard network

configuration and choose the second reserved address for the node.



Non-shared DHCP Configuration



eth1



eth1



Shared DHCP Configuration



eth2



eth2



eth3



eth0



eth0



eth0



eth1



eth1



eth0



Switch



Switch

eth0



FSP NIC



eth3



eth1



eth1



eth0



eth0



FSP NIC



Switch



eth0



eth1



eth1

Switch



Figure 12-6 Shared and non-shared DHCP configurations



12.4 High Availability configuration

On the SDMC that is intended to be the primary node, perform the procedure in

this section to configure a high availability cluster in your environment. You must

have the SMAdministrator role to configure high availability.



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12.4.1 Configuration using SDMC High Availability setup wizard

Perform the following steps:

1. Open up the IBM Systems Director Management Console GUI using a web

browser and log in as the sysadmin user. In the left navigation pane, expand

Settings and click High Availability Settings. The High Availability Settings

page opens. Click Set Up High Availability. Figure 12-7 shows the initial

page as you start the High Availability setup process.



Figure 12-7 High Availability Settings page



Note: If you do not see the Set Up High Availability button, high availability

is already configured.



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2. The Welcome page for the High Availability setup wizard (Figure 12-8) shows

the SDMC as the primary node that you are using to perform the

configuration. It reminds the user of prerequisites and provides links to

support documents for more information about High Availability. Click Next to

begin setup.



Figure 12-8 Welcome page



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3. In the Secondary Node setup page (Figure 12-9), enter the IP address or host

name and the password for the sysadmin user on that SDMC. Click Next.



Figure 12-9 Secondary Node page



4. In the Network Time Server page (not shown), specify the IP address for a

network time server or choose a primary node as the time server for both

nodes. Click Next.



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5. In the Replication IP Address page (Figure 12-10), specify the IP addresses

to use for data replication between the two nodes (one on each node). Click

Next.



Figure 12-10 Replication IP Address settings page



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6. If you want a network status IP address, determine an appropriate IP address

and enter it into the Network Status IP address page (Figure 12-11). Click

Next.

Note: A good choice for this address is the SDMCs gateway IP address.



Figure 12-11 Network Status IP address



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7. Determine the available IP address to be used as the floating IP address and

enter this address at the Floating IP Address page (Figure 12-12). Click Next.



Figure 12-12 Adding floating IP addresses



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