nvazquez opened a new pull request #2309: CLOUDSTACK-10132: Multiple Management Servers Support for agents URL: https://github.com/apache/cloudstack/pull/2309 JIRA Ticket: https://issues.apache.org/jira/browse/CLOUDSTACK-10132 Functional Specification: https://cwiki.apache.org/confluence/display/CLOUDSTACK/Multiple+Management+Servers+Support+on+agents This feature allows the direct agents to support multiple management servers. With this feature, a load balancer may no longer be necessary. The CloudStack administrator is responsible for setting a list of management servers and an algorithm in which to sort them, to the management server, using global configurations. The management server is responsible for applying algorithm to the management server list and propagate it to the agents. ### Overview A new global configuration is added: 'direct.agent.lb.algorithm'. Possible values of this global configuration are: 'static', 'roundrobin' and 'shuffle', corresponding to the algorithm that would be applied to the list of comma separated hosts defined on 'host' global configuration before sending them to the agents. - 'static': No modification is made to the original 'host' list - 'roundrobin': Rotate items one by one once the list is read - 'shuffle': Randomly sort the list A central utility is reading values from both global configurations on management server startup and is responsible of propagating list to each agent. In propagated list, the first element acts as the main host. Load balancing takes place by prepending the management server each agent should connect to, to the propagated actual list. Once agents connect to management server, they receive a comma separated string of management servers. This value is compared to their actual 'host' configuration, and in case they differ, 'host' property is updated and persisted on 'agent.properties' file with the newly received string. Reconnection logic between agent and management server is refactored as well. If agent is not able to establish a connection to its actual management server after some timeout interval, it attempts connection to the next element on its 'host' list. Also, a background task is added to the agents to attempt reconnection to their main management server in pursuit of balancing. The interval of this background task is set on 'hosts.lb.background.interval' property on 'agent.properties' file. It can be optionally disabled, by setting property to 0 ### Example Supposing an environment in which there are 3 management servers: A, B and C and 3 KVM agents. Setting 'host' = 'A,B,C', agents will receive lists depending on 'direct.agent.lb' value: - 'static': Each agent will receive the list: 'A,B,C' - 'roundrobin': First agent receives: 'A,B,C', second agent receives: 'B,C,A', third agent receives: 'C,B,A' - 'shuffle': Each agent will receive a list in random order.
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