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Hot-Standby |
Hot-Standby is a feature that allows implementing a fail-over concept in a supervisory system. This concept consists in a possibility of having two servers (main and backup), one acting as a contingency of the other, that is, if a main server fails, a backup server immediately starts executing, with no losses in this process. This is known as a Standby server.
Thus, E3 Hot-Standby tool aims at allowing a server to remain in standby, waiting for a possible failure of another server (an active server). Switching to an active server can be manual or automatic.
A manual switching is activated via E3 Admin menu on Windows Notification Area of the standby computer (the Server - Activate option). An automatic switching occurs when a standby server detects that a main server is not executing anymore. A server can assume one of the following statuses:
•Server under Maintenance: This status is indicated in Domain server's settings. A server under maintenance does not participate in any Domain event
•Active Server: Only one server can be active in a Domain at a certain time. An active server is the one executing the application (E3Run)
•Standby Server: Only one server can be in Standby mode in a Domain at a certain time. A standby server executes E3Run in Standby mode, and an application remains loaded, only waiting for a command to start operating. A backup server monitors an active server, and if it is not answering, a backup is then activated
•Inactive Server: A server switches to inactive when it is declared in a Domain, but it is neither selected as the Main nor as the Backup server. Even when inactive, this server monitors changes in a Domain file, and it may switch to an Active or Standby status if an active Domain is reconfigured
IMPORTANT |
To execute a redundant application in E3, all servers must execute the same software version, and also must have a local updated copy of Domain files (.prj, .lib, etc.). A .dom file, however, is automatically synced by E3 Server, that is, changes made to a .dom file on one server are automatically copied to this .dom file on other Domain servers. To do so, a .dom file must exist at the same path on all servers. |
Hot-Standby uses a REC connection, therefore it only works if E3 Server is started up on all computers involved in this communication.
If an E3 Studio user or a Hot-Standby user is also an Administrator of a remote computer executing E3 Server, they can remotely control this service by using services.msc, via the Action - Connect to another computer option.