Hi everyone,
I wanted to discuss how to simplify Flink's cluster level RestartStrategy
configuration [1]. Currently, Flink's behaviour with respect to configuring
the {{RestartStrategies}} is quite complicated and convoluted. The reason
for this is that we evolved the way it has been configured and wanted to
keep it backwards compatible. Due to this, we have currently the following
behaviour:
* If the config option `restart-strategy` is configured, then Flink uses
this `RestartStrategy` (so far so simple)
* If the config option `restart-strategy` is not configured, then
** If `restart-strategy.fixed-delay.attempts` or
`restart-strategy.fixed-delay.delay` are defined, then instantiate
`FixedDelayRestartStrategy(restart-strategy.fixed-delay.attempts,
restart-strategy.fixed-delay.delay)`
** If `restart-strategy.fixed-delay.attempts` and
`restart-strategy.fixed-delay.delay` are not defined, then
*** If checkpointing is disabled, then choose `NoRestartStrategy`
*** If checkpointing is enabled, then choose
`FixedDelayRestartStrategy(Integer.MAX_VALUE, "0 s")`
I would like to simplify the configuration by removing the "If
`restart-strategy.fixed-delay.attempts` or
`restart-strategy.fixed-delay.delay`, then" condition. That way, the logic
would be the following:
* If the config option `restart-strategy` is configured, then Flink uses
this `RestartStrategy`
* If the config option `restart-strategy` is not configured, then
** If checkpointing is disabled, then choose `NoRestartStrategy`
** If checkpointing is enabled, then choose
`FixedDelayRestartStrategy(Integer.MAX_VALUE, "0 s")`
That way we retain the user friendliness that jobs restart if the user
enabled checkpointing and we make it clear that any `
restart-strategy.fixed-delay.xyz` setting will only be respected if
`restart-strategy` has been set to `fixed-delay`.
This simplification would, however, change Flink's behaviour and might
break existing setups. Since we introduced `RestartStrategies` with Flink
1.0.0 and deprecated the prior configuration mechanism which enables
restarting if either the `attempts` or the `delay` has been set, I think
that the number of broken jobs should be minimal if not non-existent.
I'm sure that one can simplify the way RestartStrategies are
programmatically configured as well but for the sake of simplicity/scoping
I'd like to not touch it right away.
What do you think about this behaviour change?
[1] https://issues.apache.org/jira/browse/FLINK-13921
Cheers,
Till
