2020-08-18 11:28:26 -04:00
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.. _database-connectivity:
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*********************
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Database Connectivity
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*********************
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2020-12-23 21:08:13 +01:00
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Kea servers (kea-dhcp4 and kea-dhcp6) can be configured to use a variety of
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database backends for leases, hosts, and configuration. All of them may be
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configured to support automatic recovery when connectivity is lost (see
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2021-03-24 08:19:00 +02:00
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``max-reconnect-tries``, ``reconnect-wait-time``and
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``disable-service-on-db-loss``).
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2020-08-18 11:28:26 -04:00
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2020-12-23 21:08:13 +01:00
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It is important to understand how and when automatic recovery comes into play.
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Automatic recovery, when configured, only operates after a successful startup
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or reconfiguration during which connectivity to all backends has been
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2020-08-18 11:28:26 -04:00
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successfully established.
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2020-11-14 00:00:37 +00:00
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During server startup, the inability to connect to any of the configured
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backends is always considered fatal. A fatal error is logged and the server
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exits, based on the idea that the configuration should be valid
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at startup. Exiting to the operating system allows nanny scripts to detect
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2020-08-18 12:02:08 -04:00
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the problem.
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2020-08-18 11:28:26 -04:00
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2020-11-14 00:00:37 +00:00
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During dynamic reconfiguration, all backends are disconnected and then
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reconnected using the new configuration. If connectivity to any of the
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backends cannot be established, the server logs a fatal error but remains
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2020-12-23 21:08:13 +01:00
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up. It is able to process commands but does not serve clients. This
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2020-08-18 11:28:26 -04:00
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allows the configuration to be corrected via command, if required.
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2020-12-23 21:08:13 +01:00
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During normal operations, if connectivity to any of the backends is lost and
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2020-12-09 19:09:25 +02:00
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automatic recovery for that backend is enabled, the server disconnects from the
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respective backend and then attempts to reconnect. During the recovery process,
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2021-03-24 08:19:00 +02:00
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the server ceases to serve clients according to the
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``disable-service-on-db-loss`` configured option, and continues to respond to
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commands. If connectivity to all backends is restored, the server returns to
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normal operations. If connectivity cannot be restored after
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``max-reconnect-tries``, the server issues a fatal error and exits.
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