Incremental Deploys

As of 0.5.0 Singularity supports an incremental deploy for finer-grained control when rolling out new changes. This deploy is enabled via a few extra fields on the SingularityDeploy object when starting a deploy:

  • deployInstanceCountPerStep: Deploy this many instances at a time until the total instance count for the request is reached is reached (Optional<Integer>, default is all instances at once)
  • deployStepWaitTimeMs: Wait this many milliseconds between deploy steps before continuing to deploy the next deployInstanceCountPerStep instances (Optional<Integer>, default is 0, i.e. continue immediately)
  • autoAdvanceDeploySteps: automatically advance to the next target instance count after deployStepWaitTimeMs seconds (Optional<Boolean>, defaults to true). If this is false, then manual confirmation will be needed to move to the next target instance count. This can be done via the ui.

Example

TestService is currently running 3 instances. During the next deploy, you want to replace only 1 of these instances at a time and have Singularity wait at least a minute after deploying one so you can verify that everything works as expected. The following fields can be added to the deploy json to accomplish this:

deployInstanceCountPerStep: 1
deployStepWaitTimeMs: 60000
autoAdvanceDeploySteps: true

When the deploy starts, Singularity will start 1 (deployInstanceCountPerStep) instance from the new deploy (The 3 old instances will still be running). Once the new task is determined to be healthy a few things happen:

  • Singularity will add the instance from the new deploy to the load balancer (if applicable)
  • Singularity will shut down 1 (deployInstanceCountPerStep) of the instances from the old deploy after removing it from the load balancer (if applicable)
  • Singularity will start counting down the 60000 ms until it launches the next deployInstanceCountPerStep instances

Once the deployStepWaitTimeMs of wait time has elapsed, Singularity will start this process again, launching a second task for the new deploy, waiting until it is healthy, then shutting down a task from the old deploy. This will continue until the deploy fails, the deploy is cancelled, or all instances are part of the new deploy and it succeeds.

A few more things to note about the incremental deploy process:

  • If the deploy fails or is cancelled, Singularity replaces any missing instances from the old deploy and makes sure they are healthy before shutting down active/healthy instances from the new deploy. (i.e. you will never be under capacity)
  • At any time, it is possible to advance the deploy to another target instance count via the UI or API. In other words, you can skip the remaining deployStepWaitTimeMs, skip steps of the deploy, or even decrease the instance count to roll back a step.

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