Primary and backup servers cluster two-level failover
WebSphere V5 supplies a two-level failover functionality. When the plugin-cfg.xml is generated, all servers are initially listed under the PrimaryServers tag. You can manually move selected servers to be listed under the BackupServers tag, as shown in Example 9-1.
Example 9-1 Primary and Backup Server lists in plugin-cfg.xml
<PrimaryServers>
<Server Name="HAClusterServer1"/>
<Server Name="HAClusterServer3"/>
</PrimaryServers>
<BackupServers>
Server Name="HAClusterServer2"/>
<Server Name="HAClusterServer4"/>
</BackupServers>
The Web server plug-in will not route requests to any server in the Backup Server list as long as there are appservers available from the Primary Server list. Within the PrimaryServers, the plug-in routes traffic according to server weight and/or session affinity. When all servers in the Primary Server list are unavailable, the plug-in will route traffic to the first available server in the Backup Server list. If the first server in the Backup Server list is not available, the request will be routed to the next server in the Backup Server list. Weighted round robin routing is not performed for the servers in the Backup Server list. The plug-in just uses one server at a time. Refer to Primary and backup servers for more details on how the plug-in performs the server selection.
This two-level failover mechanism provides more advanced failover support, allowing better use of available server capacity.
Typical two-level failover behavior is shown in the trace in Example 9-2.
Example 9-2 Two-level failover trace
TRACE: ws_server_group: serverGroupAddPrimaryServerName: adding WebHAbbMember1 to primary server list
TRACE: ws_server_group: serverGroupAddPrimaryServerName: adding WebHAbbMember3 to primary server list
TRACE: ws_server_group: serverGroupAddBackupServerName: adding WebHAbbMember2 to backup server list
TRACE: ws_server_group: serverGroupAddBackupServerName: adding WebHAbbMember4 to backup server list
TRACE: ws_server_group: serverGroupGetFirstServer: getting the first server
TRACE: ws_server_group: serverGroupGetNextServer: getting the next server
Only primary servers participate weighted Round Robin:
TRACE: ws_server_group: serverGroupNextRoundRobinServer: Round Robin load balancing
TRACE: ws_server_group: serverGroupNextRoundRobinServer: numPrimaryServers is 2
TRACE: ws_server_group: assureWeightsValid: group WebHACluster
TRACE: ws_server_group: serverGroupGetFirstPrimaryServer: getting the first primary server
TRACE: ws_server_group: sum_wlb_weights: WebHAbbMember1: 1 max, 0 cur.
TRACE: ws_server_group: serverGroupGetNextPrimaryServer: getting the next primary server
TRACE: ws_server_group: sum_wlb_weights: WebHAbbMember3: 1 max, 0 cur.
TRACE: ws_server_group: serverGroupGetNextPrimaryServer: getting the next primary server
TRACE: ws_server_group: sum_wlb_weights := 0
TRACE: ws_server_group: serverGroupGetFirstServer: getting the first server
TRACE: ws_server_group: serverGroupGetNextServer: getting the next server
TRACE: ws_server_group: serverGroupGetNextServer: getting the next server
TRACE: ws_server_group: serverGroupGetNextServer: getting the next server
TRACE: ws_server_group: serverGroupGetNextServer: getting the next server
--------------Retry another one
TRACE: ws_server_group: serverGroupCheckServerStatus: Checking status of WebHAbbMember3, ignoreWeights 0, markedDown 1, retryNow 1, wlbAllows 1
TRACE: ws_server_group: serverGroupCheckServerStatus: Time to retry server WebHAbbMember3
TRACE: ws_server_group: lockedServerGroupUseServer: Server WebHAbbMember3 picked, weight 0.
TRACE: ws_common: websphereFindTransport: Finding the transport
TRACE: ws_common: websphereFindTransport: Setting the transport: 10.55.90.84 on port 9081
TRACE: ws_common: websphereExecute: Executing the transaction with the app server
TRACE: ws_common: websphereGetStream: Getting the stream to the app server
TRACE: ws_transport: transportStreamDequeue: Checking for existing stream from the queue
ERROR: ws_common: websphereGetStream: Failed to connect to app server, OS err=10061
ERROR: ws_common: websphereExecute: Failed to create the stream
ERROR: ws_server: serverSetFailoverStatus: Marking WebHAbbMember3 down
ERROR: ws_common: websphereWriteRequestReadResponse: Failed to execute the transaction to 'WebHAbbMember3'; will try another one
TRACE: ws_server_group: serverGroupNextRoundRobinServer: Round Robin load balancing
TRACE: ws_server_group: serverGroupNextRoundRobinServer: numPrimaryServers is 2
TRACE: ws_server_group: assureWeightsValid: group WebHACluster
TRACE: ws_server_group: serverGroupGetFirstPrimaryServer: getting the first
-----------------Get backup Server
TRACE: ws_server_group: serverGroupGetFirstPrimaryServer: getting the first primary server
TRACE: ws_server_group: serverGroupCheckServerStatus: Checking status of WebHAbbMember1, ignoreWeights 0, markedDown 1, retryNow 0, wlbAllows 1
TRACE: ws_server_group: serverGroupCheckServerStatus: Server WebHAbbMember1 is marked down; retry in 60
ERROR: ws_server_group: serverGroupNextRoundRobinServer: Failed to find a server; all could be down
TRACE: ws_server_group: serverGroupGetNextUpBackupServer: Getting the next up backup server
TRACE: ws_server_group: serverGroupGetFirstBackupServer: getting the first backup server
TRACE: ws_server_group: serverGroupCheckServerStatus: Checking status of WebHAbbMember2, ignoreWeights 1, markedDown 0, retryNow 0, wlbAllows 1
TRACE: ws_common: websphereFindTransport: Finding the transport
TRACE: ws_common: websphereFindTransport: Setting the transport:
10.55.90.22 on port 9082
TRACE: ws_common: websphereExecute: Executing the transaction with the app server
TRACE: ws_common: websphereGetStream: Getting the stream to the app server
TRACE: ws_transport: transportStreamDequeue: Checking for existing stream from the queue
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