Difference between revisions of "CentOS Cluster Configuration"
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| + | =WORK IN PROGRESS - ARTICLE NOT FINISHED= | ||
| + | __TOC__ | ||
=cluster.conf configuration file= | =cluster.conf configuration file= | ||
Configuration file for: | Configuration file for: | ||
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*rgmanager - Resource Group manager configuration. Fx. apache service setup on cluster. | *rgmanager - Resource Group manager configuration. Fx. apache service setup on cluster. | ||
See [http://sources.redhat.com/cluster/doc/cluster_schema_rhel5.html RedHAT 5 cluster scheme] | See [http://sources.redhat.com/cluster/doc/cluster_schema_rhel5.html RedHAT 5 cluster scheme] | ||
| − | =cman - | + | =cman - Basic cluster config= |
| + | |||
=fence - Fencing nodes= | =fence - Fencing nodes= | ||
=dlm - lock management= | =dlm - lock management= | ||
=gfs - global file system= | =gfs - global file system= | ||
=rgmanager - resource config= | =rgmanager - resource config= | ||
| − | Resource Group manager is a High Availability service. Rgmanager can start and stop services on nodes. If a service is failing on one node it will be started on another node. Rgmanager monitor the services and make sure they are actually runnning. | + | Resource Group manager is a High Availability service. Rgmanager can start and stop services on nodes. If a service is failing on one node it will be started on another node. Rgmanager monitor the services and make sure they are actually runnning.<br/> |
| + | The ''rgmanager'' service must run on all nodes participating in a ''service group''. | ||
== Service Groups == | == Service Groups == | ||
A ''Service Group'' is a group of nodes on which a specified service can be started or stopped by rgmanager. Not all nodes in a cluster need to be member of a ''Service Group''. There can be many ''Service Groups'' in a cluster.If a service fails, a script is called to automatically restart the service. If a node fails, the service may be relocated to a different node in the service group. | A ''Service Group'' is a group of nodes on which a specified service can be started or stopped by rgmanager. Not all nodes in a cluster need to be member of a ''Service Group''. There can be many ''Service Groups'' in a cluster.If a service fails, a script is called to automatically restart the service. If a node fails, the service may be relocated to a different node in the service group. | ||
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A Cluster-service is a resource that are shared among nodes. For example a ''apache'' WEB-service. This service can be run in two different ways. | A Cluster-service is a resource that are shared among nodes. For example a ''apache'' WEB-service. This service can be run in two different ways. | ||
===active-passive Cluster-service=== | ===active-passive Cluster-service=== | ||
| − | An active-passive Cluster-service is a service running on one node at a time. If the node running the service fails the service is started on another node in the Service Group. | + | An ''active-passive'' Cluster-service is a service running on one node at a time. If the node running the service fails the service is started on another node in the Service Group. |
====active-passive example==== | ====active-passive example==== | ||
| − | + | Three ''front-end-nodes'' have the responsibility of delivering a high-availability WEB-service. In the image below there are three services | |
{| | {| | ||
|- | |- | ||
|valign="top"| | |valign="top"| | ||
| + | ===== Picture 1 - Normal operation ===== | ||
#Filesystem: The filesystem is a [[ext3]] filesystem which can only be mounted on one node at a time. In Picture 1 below the left node has mounted the shared filesystem on the SCSI-raid controllers. The other servers has not mounted the shared filesystem. | #Filesystem: The filesystem is a [[ext3]] filesystem which can only be mounted on one node at a time. In Picture 1 below the left node has mounted the shared filesystem on the SCSI-raid controllers. The other servers has not mounted the shared filesystem. | ||
#Service: The Apache WEB-server service is running on the left node, and using the resources from the shared SCSI filesystem delivering WEB-content to the Internet. The Apache service on the other nodes are stopped. | #Service: The Apache WEB-server service is running on the left node, and using the resources from the shared SCSI filesystem delivering WEB-content to the Internet. The Apache service on the other nodes are stopped. | ||
#IP address: The left server is answering request for the shared IP address 80.1.2.3. The other nodes ignores 80.1.2.3. | #IP address: The left server is answering request for the shared IP address 80.1.2.3. The other nodes ignores 80.1.2.3. | ||
| + | ===== Picture 2 - Fault in left node ===== | ||
| + | When an error is discovered by the ''rgmanager'' on the failing node, ''rgmanager'' communicates with the ''rgmanager'' on the other nodes and decide which other node should transition from ''passive'' to ''active''. In the example on Picture 2, the middle node goes to active and continues to server WEB-requests to 80.1.2.3. | ||
| + | ====== Transition steps in example ====== | ||
| + | When the ''rgmanager'' on the left discover an error on the left node it will, | ||
| + | *Stop the apache server, unmount the shared file system and release the virtual IP address 80.1.2.3. The order is configurable. | ||
| + | *Communicating to the other ''rgmanager''s on the other nodes and deciding which node should be active. | ||
| + | *Optionally get ''fenced'' shut down the failing node, eventually by removing power to it. (Then we are sure all resources are released - IP address and filesystem) | ||
| + | |||
|valign="top"| | |valign="top"| | ||
|[[Image:Cluster active-passive.png|200px|thumb|Picture 1: Active-passive example]] | |[[Image:Cluster active-passive.png|200px|thumb|Picture 1: Active-passive example]] | ||
|[[Image:Cluster active-passive fail.png|200px|thumb|Picture 2: Active failed example]] | |[[Image:Cluster active-passive fail.png|200px|thumb|Picture 2: Active failed example]] | ||
| + | |- | ||
| + | |} | ||
| + | ===active-active Cluster-service=== | ||
| + | An ''active-active'' Cluster-service is a service running on all the nodes at the same time. If a node fails the other nodes takes over the load. | ||
| + | ====active-active example==== | ||
| + | Three ''front-end-nodes'' have the responsibility of delivering a high-availability and high-load WEB-service. | ||
| + | {| | ||
| + | |- | ||
| + | |valign="top"| | ||
| + | ===== Picture 3 - Normal operation ===== | ||
| + | #Filesystem: The filesystem is a [[GFS]] filesystem which can be mounted on several nodes on the same time. In Picture 3 WEB requests from the Internet to 80.1.2.3 are distributed to the WEB-server nodes 10.2.2.1, 10.2.2.2 and 10.2.2.3 in a ''Round Robin'' fashion by the ''Load Balancer'' so each server is serving 1/3 of the requests. Of course the ''Load balancer'' should be redundant. | ||
| + | ===== Picture 4 - Fault in left node ===== | ||
| + | When an error is discovered the failing node should be fenced, and | ||
| + | *Either the ''Load Balancer'' should stop sending requests to 10.2.2.1 or | ||
| + | *One of the other nodes should start also serving requests for 10.2.2.1 | ||
| + | |||
| + | |valign="top"| | ||
| + | |[[Image:Cluster active-active.png|200px|thumb|Picture 3: Active-Active example]] | ||
| + | |[[Image:Cluster active-active fail.png|200px|thumb|Picture 4: A Active failed example]] | ||
|- | |- | ||
|} | |} | ||
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*''clustat'' - See cluster and service status ''clustat -s SERVICE_NAME -l'' | *''clustat'' - See cluster and service status ''clustat -s SERVICE_NAME -l'' | ||
*[http://sources.redhat.com/cluster/wiki/FAQ/RGManager RedHAT rgmanager FAQ] | *[http://sources.redhat.com/cluster/wiki/FAQ/RGManager RedHAT rgmanager FAQ] | ||
| + | [[category:linux]][[category:cluster]][[Category:CentOS]] | ||
Latest revision as of 13:32, 8 November 2009
WORK IN PROGRESS - ARTICLE NOT FINISHED
Contents
- 1 WORK IN PROGRESS - ARTICLE NOT FINISHED
- 2 cluster.conf configuration file
- 3 cman - Basic cluster config
- 4 fence - Fencing nodes
- 5 dlm - lock management
- 6 gfs - global file system
- 7 rgmanager - resource config
cluster.conf configuration file
Configuration file for:
- cman - Cluster configuration
- fence - Fence configuration for disabling nodes with errors
- dlm - Distributed Lock Manager Configuration. Rules for access to shared resources
- gfs - Global file System configuration. Shared file systems among nodes.
- rgmanager - Resource Group manager configuration. Fx. apache service setup on cluster.
cman - Basic cluster config
fence - Fencing nodes
dlm - lock management
gfs - global file system
rgmanager - resource config
Resource Group manager is a High Availability service. Rgmanager can start and stop services on nodes. If a service is failing on one node it will be started on another node. Rgmanager monitor the services and make sure they are actually runnning.
The rgmanager service must run on all nodes participating in a service group.
Service Groups
A Service Group is a group of nodes on which a specified service can be started or stopped by rgmanager. Not all nodes in a cluster need to be member of a Service Group. There can be many Service Groups in a cluster.If a service fails, a script is called to automatically restart the service. If a node fails, the service may be relocated to a different node in the service group.
What is a Cluster-service
A Cluster-service is a resource that are shared among nodes. For example a apache WEB-service. This service can be run in two different ways.
active-passive Cluster-service
An active-passive Cluster-service is a service running on one node at a time. If the node running the service fails the service is started on another node in the Service Group.
active-passive example
Three front-end-nodes have the responsibility of delivering a high-availability WEB-service. In the image below there are three services
Picture 1 - Normal operation
Picture 2 - Fault in left nodeWhen an error is discovered by the rgmanager on the failing node, rgmanager communicates with the rgmanager on the other nodes and decide which other node should transition from passive to active. In the example on Picture 2, the middle node goes to active and continues to server WEB-requests to 80.1.2.3. Transition steps in exampleWhen the rgmanager on the left discover an error on the left node it will,
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active-active Cluster-service
An active-active Cluster-service is a service running on all the nodes at the same time. If a node fails the other nodes takes over the load.
active-active example
Three front-end-nodes have the responsibility of delivering a high-availability and high-load WEB-service.
Picture 3 - Normal operation
Picture 4 - Fault in left nodeWhen an error is discovered the failing node should be fenced, and
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files and programs
- /usr/share/cluster - here lives the rgmanager scripts
- /etc/cluster/cluster.conf - rgmanager configuration
- clustat - See cluster and service status clustat -s SERVICE_NAME -l
- RedHAT rgmanager FAQ