Step 5: Test the cluster step by step - Amazon EMR
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Step 5: Test the cluster step by step

A useful technique when you are trying to track down the source of an error is to restart the cluster and submit the steps to it one by one. This lets you check the results of each step before processing the next one, and gives you the opportunity to correct and re-run a step that has failed. This also has the advantage that you only load your input data once.

To test a cluster step by step
  1. Launch a new cluster, with both keep alive and termination protection enabled. Keep alive keeps the cluster running after it has processed all of its pending steps. Termination protection prevents a cluster from shutting down in the event of an error. For more information, see Configuring a cluster to continue or terminate after step execution and Using termination protection.

  2. Submit a step to the cluster. For more information, see Submit work to a cluster.

  3. When the step completes processing, check for errors in the step log files. For more information, see Step 4: Examine the log files. The fastest way to locate these log files is by connecting to the master node and viewing the log files there. The step log files do not appear until the step runs for some time, finishes, or fails.

  4. If the step succeeded without error, run the next step. If there were errors, investigate the error in the log files. If it was an error in your code, make the correction and re-run the step. Continue until all steps run without error.

  5. When you are done debugging the cluster, and want to terminate it, you will have to manually terminate it. This is necessary because the cluster was launched with termination protection enabled. For more information, see Using termination protection.