Restart Strategies

Flink supports different restart strategies which control how the jobs are restarted in case of a failure. The cluster can be started with a default restart strategy which is always used when no job specific restart strategy has been defined. In case that the job is submitted with a restart strategy, this strategy overrides the cluster’s default setting.

The default restart strategy is set via Flink’s configuration file flink-conf.yaml. The configuration parameter restart-strategy defines which strategy is taken. Per default, the no-restart strategy is used. See the following list of available restart strategies to learn what values are supported.

Each restart strategy comes with its own set of parameters which control its behaviour. These values are also set in the configuration file. The description of each restart strategy contains more information about the respective configuration values.

Restart Strategy	Value for restart-strategy
Fixed delay	fixed-delay
Failure rate	failure-rate
No restart	none

Apart from defining a default restart strategy, it is possible to define for each Flink job a specific restart strategy. This restart strategy is set programmatically by calling the setRestartStrategy method on the ExecutionEnvironment. Note that this also works for the StreamExecutionEnvironment.

The following example shows how we can set a fixed delay restart strategy for our job. In case of a failure the system tries to restart the job 3 times and waits 10 seconds in-between successive restart attempts.

ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setRestartStrategy(RestartStrategies.fixedDelayRestart(
  3, // number of restart attempts
  Time.of(10, TimeUnit.SECONDS) // delay
));

val env = ExecutionEnvironment.getExecutionEnvironment()
env.setRestartStrategy(RestartStrategies.fixedDelayRestart(
  3, // number of restart attempts
  Time.of(10, TimeUnit.SECONDS) // delay
))

Fixed Delay Restart Strategy

The fixed delay restart strategy attempts a given number of times to restart the job. If the maximum number of attempts is exceeded, the job eventually fails. In-between two consecutive restart attempts, the restart strategy waits a fixed amount of time.

This strategy is enabled as default by setting the following configuration parameter in flink-conf.yaml.

restart-strategy: fixed-delay

Configuration Parameter	Description	Default Value
restart-strategy.fixed-delay.attempts	Number of restart attempts	1
restart-strategy.fixed-delay.delay	Delay between two consecutive restart attempts	akka.ask.timeout

restart-strategy.fixed-delay.attempts: 3
restart-strategy.fixed-delay.delay: 10 s

The fixed delay restart strategy can also be set programmatically:

ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setRestartStrategy(RestartStrategies.fixedDelayRestart(
  3, // number of restart attempts
  Time.of(10, TimeUnit.SECONDS) // delay
));

val env = ExecutionEnvironment.getExecutionEnvironment()
env.setRestartStrategy(RestartStrategies.fixedDelayRestart(
  3, // number of restart attempts
  Time.of(10, TimeUnit.SECONDS) // delay
))

Restart Attempts

The number of times that Flink retries the execution before the job is declared as failed is configurable via the restart-strategy.fixed-delay.attempts parameter.

The default value is 1.

Retry Delays

Execution retries can be configured to be delayed. Delaying the retry means that after a failed execution, the re-execution does not start immediately, but only after a certain delay.

Delaying the retries can be helpful when the program interacts with external systems where for example connections or pending transactions should reach a timeout before re-execution is attempted.

The default value is the value of akka.ask.timeout.

Failure Rate Restart Strategy

The failure rate restart strategy restarts job after failure, but when failure rate (failures per time interval) is exceeded, the job eventually fails. In-between two consecutive restart attempts, the restart strategy waits a fixed amount of time.

This strategy is enabled as default by setting the following configuration parameter in flink-conf.yaml.

restart-strategy: failure-rate

Configuration Parameter	Description	Default Value
restart-strategy.failure-rate.max-failures-per-interval	Maximum number of restarts in given time interval before failing a job	1
restart-strategy.failure-rate.failure-rate-interval	Time interval for measuring failure rate.	1 minute
restart-strategy.failure-rate.delay	Delay between two consecutive restart attempts	akka.ask.timeout

restart-strategy.failure-rate.max-failures-per-interval: 3
restart-strategy.failure-rate.failure-rate-interval: 5 min
restart-strategy.failure-rate.delay: 10 s

The failure rate restart strategy can also be set programmatically:

ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setRestartStrategy(RestartStrategies.failureRateRestart(
  3, // max failures per interval
  Time.of(5, TimeUnit.MINUTES), //time interval for measuring failure rate
  Time.of(10, TimeUnit.SECONDS) // delay
));

val env = ExecutionEnvironment.getExecutionEnvironment()
env.setRestartStrategy(RestartStrategies.failureRateRestart(
  3, // max failures per unit
  Time.of(5, TimeUnit.MINUTES), //time interval for measuring failure rate
  Time.of(10, TimeUnit.SECONDS) // delay
))

No Restart Strategy

The job fails directly and no restart is attempted.

restart-strategy: none

The no restart strategy can also be set programmatically:

ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setRestartStrategy(RestartStrategies.noRestart());

val env = ExecutionEnvironment.getExecutionEnvironment()
env.setRestartStrategy(RestartStrategies.noRestart())

Fallback Restart Strategy

The cluster defined restart strategy is used. This helpful for streaming programs which enable checkpointing. Per default, a fixed delay restart strategy is chosen if there is no other restart strategy defined.