Automatically retry an action after an error
Problem
You want to retry an action after an error is thrown.
Solution
Use the Catch node to receive the error and connect it
back to the node that needs to retry the action.
Example
[{"id":"27e61f12.c1a15","type":"inject","z":"fc046f99.4be08","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":100,"y":320,"wires":[["d7d08440.31b678"]]},{"id":"d7d08440.31b678","type":"function","z":"fc046f99.4be08","name":"Random error","func":"// Randomly throw an error rather than\n// pass on message.\nif (Math.random() < 0.5) {\n node.error(\"a random error\", msg);\n} else {\n return msg;\n}","outputs":1,"noerr":0,"x":320,"y":320,"wires":[["f22b1e9a.5d89b"]]},{"id":"f22b1e9a.5d89b","type":"debug","z":"fc046f99.4be08","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":510,"y":320,"wires":[]},{"id":"2166290d.98d736","type":"delay","z":"fc046f99.4be08","name":"","pauseType":"delay","timeout":"2","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"x":240,"y":380,"wires":[["d7d08440.31b678"]]},{"id":"139b836e.7950ed","type":"catch","z":"fc046f99.4be08","name":"","scope":["d7d08440.31b678"],"uncaught":false,"x":90,"y":380,"wires":[["2166290d.98d736","9c8ab214.0ecaa"]]},{"id":"9c8ab214.0ecaa","type":"debug","z":"fc046f99.4be08","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"error","targetType":"msg","x":240,"y":440,"wires":[]}]
Discussion
Some errors are transitory and an action simply needs to be retried in order to succeed. Alternatively, there may be some remedial action needed before retrying.
In the example flow, a Function simulates a random
error - there is a 50% chance it will throw an error rather than pass on the message.
The Catch receives the error which passes the message
back to the Function node to retry. It also includes
a Delay node as, in some circumstances, it is suitable
to wait for a short interval before retrying.
