Coming soon: Updated Lambda states lifecycle for VPC networking

On November 27, we announced that AWS Lambda now includes additional attributes in the function information returned by several Lambda API actions to better communicate the current “state” of your function, when they are being created or updated. In our post “Tracking the state of AWS Lambda functions”, we covered the various states your Lambda function can be in, the conditions that lead to them, and how the Lambda service transitions the function through those states.

Our first feature using the function states lifecycle is a change to the recently announced improved VPC networking for AWS Lambda functions. As stated in the announcement post, Lambda creates the ENIs required for your function to connect to your VPCs, which can take 60–90 seconds to complete. We are updating this operation to explicitly place the function into a Pending state while pre-creating the required elastic network interface resources, and transitioning to an Active state after that process is completed. By doing this, we can use the lifecycle to complete the creation of these resources, and then reduce inconsistent invokes after the create/update has completed.

Most customers experience no impact from this change except for fewer long cold-starts due to network resource creation. As a reminder, any invocations or other API actions that operate on the function will fail during the time before the function is Active. To better assist you in adopting this behavior, we are rolling out this behavior for VPC configured functions in a phased manner. This post provides further details about timelines and approaches to both test the change before it is 100% live or delay it for your functions using a delay mechanism.

Changes to function create and update

On function create

During creation of new functions configured for VPC, your function remains in the Pending state until all VPC resources are created. You are not able to invoke the function or take any other Lambda API actions against it. After successful completion of the creation of these resources, your function transitions automatically to the Active state and is available for invokes and Lambda API actions. If the network resources fail to create then your function is placed in a Failed state.

On function update

During the update of functions configured for VPC, if there are any modifications to the VPC configuration, the function remains in the Active state, but shows in the InProgress status until all VPC resources are updated. During this time, any invokes go to the previous function code and configuration. After successful completion, the function LastUpdateStatus transitions automatically to Successful and all new invokes use the newly updated code and configuration. If the network resources fail to be created/updated then the LastUpdateStatus shows Failed, but the previous code and configuration remains in the Active state.

It’s important to note that creation or update of VPC resources can take between 60-90 seconds complete.

Change timeframe

As a reminder, all functions today show an Active state only. We are rolling out this change to create resources during the Pending state over a multiple phase period starting with the Begin Testing phase today, December 16, 2019. The phases allow you to update tooling for deploying and managing Lambda functions to account for this change. By the end of the update timeline, all accounts transition to using this new VPC resource create/update Lambda lifecycle.

Update timeline

December 16, 2019 – Begin Testing: You can now begin testing and updating any deployment or management tools you have to account for the upcoming lifecycle change. You can also use this time to update your function configuration to delay the change until the Delayed Update phase.

January 20, 2020 – General Update: All customers without the delayed update configuration begin seeing functions transition as described above under “On function create” and “On function update”.

February 17, 2020 – Delayed Update: The delay mechanism expires and customers now see the new VPC resource lifecycle applied during function create or update.

March 2, 2020 – Update End: All functions now have the new VPC resource lifecycle applied during function create or update.

Opt-in and delayed update configurations

Starting today, we are providing a mechanism for an opt-in, to allow you to update and test your tools and developer workflow processes for this change. We are also providing a mechanism to delay this change until the end of the Delayed Update phase. If you configure your functions for VPC and use the delayed update mechanism after the start of the General Update, your functions continue to experience a delayed first invocation due to VPC resource creation.

This mechanism operates on a function-by-function basis, so you can test and experiment individually without impacting your whole account. Once the General Update phase begins, all functions in an account that do not have the delayed update mechanism in place see the new lifecycle for their functions.

Both mechanisms work by adding a special string in the “Description” parameter of your Lambda functions. This string can be added to the prefix or suffix, or be the entire contents of the field.

To opt in:

aws:states:opt-in

To delay the update:

aws:states:opt-out

NOTE: Delay configuration mechanism has no impact after the Delayed Update phase ends.

Here is how this looks in the console:

1. I add the opt-in configuration to my function’s Description.
   

   Opt-in in Description

2. When I choose Save at the top, I see the update begin. During this time, I am blocked from executing tests, updating my code, and making some configuration changes against the function.
   

   Function updating

3. After the update completes, I can once again run tests and other console commands.
   

   Function update successful

Once the opt-in is set for a function, then updates on that function go through the update flow shown above. If I don’t change my function’s VPC configuration, then updates to my function transition almost instantly to the Successful update status.

With this in place, you can now test your development workflow ahead of the General Update phase. Download the latest CLI (version 1.16.291 or greater) or SDKs in order to see function state and related attribute information.

Conclusion

With functions states, you can have better clarity on how the resources required by your Lambda function are being created. This change does not impact the way that functions are invoked or how your code is executed. While this is a minor change to when resources are created for your Lambda function, the result is even better consistency of performance. Combined with the original announcement of improved VPC networking for Lambda, you experience better consistency for invokes, greatly reduced cold-starts, and fewer network resources created for your functions.