Sample Configuration: Complex Four-Node Cluster
The cluster in this example has two large enterprise servers (LargeServer1 and LargeServer2) and two medium-sized servers (MedServer1 and MedServer2). It has four service groups, G1 through G4, with various loads and prerequisites. Groups G1 and G2 are database applications with specific shared memory and semaphore requirements. Groups G3 and G4 are middle-tier applications with no specific memory or semaphore requirements.
include "types.cf"
cluster SGWM-demo (
)
system LargeServer1 (
Capacity = 200
Limits = { ShrMemSeg=20, Semaphores=10, Processors=12 }
LoadWarningLevel = 90
LoadTimeThreshold = 600
)
system LargeServer2 (
Capacity = 200
Limits = { ShrMemSeg=20, Semaphores=10, Processors=12 }
LoadWarningLevel=70
LoadTimeThreshold=300
)
system MedServer1 (
Capacity = 100
Limits = { ShrMemSeg=10, Semaphores=5, Processors=6 }
)
system MedServer2 (
Capacity = 100
Limits = { ShrMemSeg=10, Semaphores=5, Processors=6 }
)
group G1 (
SystemList = { LargeServer1, LargeServer2, MedServer1, MedServer2 }
SystemZones = { LargeServer1=0, LargeServer2=0, MedServer1=1,
MedServer2=1 }
AutoStartPolicy = Load
AutoStartList = { LargeServer1, LargeServer2 }
FailOverPolicy = Load
Load = 100
Prerequisites = { ShrMemSeg=10, Semaphores=5, Processors=6 }
)
group G2 (
SystemList = { LargeServer1, LargeServer2, MedServer1, MedServer2 }
SystemZones = { LargeServer1=0, LargeServer2=0, MedServer1=1,
MedServer2=1 }
AutoStartPolicy = Load
AutoStartList = { LargeServer1, LargeServer2 }
FailOverPolicy = Load
Load = 100
Prerequisites = { ShrMemSeg=10, Semaphores=5, Processors=6 }
)
group G3 (
SystemList = { LargeServer1, LargeServer2, MedServer1, MedServer2 }
SystemZones = { LargeServer1=0, LargeServer2=0, MedServer1=1,
MedServer2=1 }
AutoStartPolicy = Load
AutoStartList = { MedServer1, MedServer2 }
FailOverPolicy = Load
Load = 30
)
group G4 (
SystemList = { LargeServer1, LargeServer2, MedServer1, MedServer2 }
SystemZones = { LargeServer1=0, LargeServer2=0, MedServer1=1,
MedServer2=1 }
AutoStartPolicy = Load
AutoStartList = { MedServer1, MedServer2 }
FailOverPolicy = Load
Load = 20
)
AutoStart Operation
In this configuration, the AutoStart sequence resembles:
G1---LargeServer1
G2---LargeServer2
G3---MedServer1
G4---MedServer2
All groups begin a probe sequence when the cluster starts. Groups G1 and G2 have an AutoStartList of LargeServer1 and LargeServer2. When these groups probe, they are queued to go online on one of these servers, based on highest AvailableCapacity value. If G1 probes first, it chooses LargeServer1 because LargeServer1 and LargeServer2 both have an AvailableCapacity of 200, but LargeServer1 is lexically first. Groups G3 and G4 use the same algorithm to determine their servers.
Normal Operation
The configuration resembles:
| Server
|
AvailableCapacity
|
CurrentLimits
|
Online Groups
|
|---|
LargeServer1
|
100
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G1
|
LargeServer2
|
100
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G2
|
MedServer1
|
70
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G3
|
MedServer2
|
80
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G4
|
Failure Scenario
In this scenario, if LargeServer2 fails, VCS scans all available systems in group G2's SystemList that are in the same SystemZone and creates a subset of systems that meet the group's prerequisites. In this case, LargeServer1 meets all required Limits. Group G2 is brought online on LargeServer1. This results in the following configuration:
| Server
|
AvailableCapacity
|
CurrentLimits
|
Online Groups
|
|---|
LargeServer1
|
0
|
ShrMemSeg=0
Semaphores=0
Processors=0
|
G1, G2
|
MedServer1
|
70
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G3
|
MedServer2
|
80
|
ShrMemSeg=10
Semaphores=5
Processors=6
|
G4
|
After 10 minutes (LoadTimeThreshold = 600) VCS fires the loadwarning trigger on LargeServer1 because the LoadWarningLevel exceeds 90 percent.
Cascading Failure Scenario
In this scenario, another system failure can be tolerated because each system has sufficient Limits to accommodate the service group running on its peer. If MedServer1 fails, its groups can fail over to MedServer2.
If LargeServer1 fails, the failover of the two groups running on it is serialized. The first group lexically, G1, chooses MedServer2 because the server meets the required Limits and has AvailableCapacity value. Group G2 chooses MedServer1 because it is the only remaining system that meets the required Limits.
|
