RUST + AWS AppConfig

In this post, I show you how to load a config dynamically and as fastest as possible.

You have two options to load your config with AppConfig:

• Lambda Extension - this example
• Using the SDK with the GetConfiguration

NOTE: Not even AWS updated his page, but RUST support it and unless they will add it, there is no example out there.

AppConfig theory

AppConfig in practise

By default, you have 1000 TPS, and in a serverless world, it is easy to reach it. You can request an increase of quota opening a ticket

After the first request, the profile is cached, and so from now on, you hit the internal cache of AppConfig. What I have noticed is that even if you have this in place when you reach the 1000 TPS, you will get an error like invalid JSON response body at http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfilereason: Unexpected token R in JSON at position 0

It does not matter that you used to retry. It is like cached, and so you cannot escape this problem. However, the retry is useful when AppConfig returns A 504 Gateway Timeout Error.

The solution is to leverage the Lambda context and call AppConfig only once until this Lambda exists:

• reducing the call to AppConfig cache
• speeding up your Lambda
• saving cents

AppConfig hitting their CACHE

EXECUTION 1 - COLD START

START RequestId: daefa720-eab3-40d9-b982-db2f52002bfb Version: $LATEST
[appconfig agent] INFO AppConfig Lambda Extension 2.0.15
[appconfig agent] INFO serving on port 2772
EXTENSION Name: AppConfigAgent State: Ready Events: [INVOKE,SHUTDOWN]

we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: daefa720-eab3-40d9-b982-db2f52002bfb Duration: 286.35

EXECUTION 2 - WARM STATE

START RequestId: 1d66614c-3272-40ec-a17b-dea81c353097 Version: $LATEST
we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: 1d66614c-3272-40ec-a17b-dea81c353097 Duration: 192.21 ms 

EXECUTION 3 - WARM STATE

START RequestId: d7b1508e-e95f-4f49-9b44-f5768372a674 Version: $LATEST
we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: d7b1508e-e95f-4f49-9b44-f5768372a674 Duration: 187.56 ms

Using the Lambda Context

EXECUTION 1 - COLD START

START RequestId: cd5ccc81-6ff5-4fa2-8a38-e708e833cde9 Version: $LATEST
[appconfig agent] INFO AppConfig Lambda Extension 2.0.15
[appconfig agent] INFO serving on port 2772
EXTENSION Name: AppConfigAgent State: Ready Events: [INVOKE,SHUTDOWN]

we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: cd5ccc81-6ff5-4fa2-8a38-e708e833cde9 Duration: 475.24

EXECUTION 2 - WARM STATE

START RequestId: d1f74efe-6ce2-4879-9374-b68535fb8e95 Version: $LATEST
we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: d1f74efe-6ce2-4879-9374-b68535fb8e95 Duration: 3.79 ms

EXECUTION 3 - WARM STATE

START RequestId: 36db9855-74cf-4c3c-a560-c1baae94d96a Version: $LATEST
we get the config
INFO [handler] URL "http://localhost:2772/applications/MyTestApplication/environments/MyTestEnvironment/configurations/MyTestProfile"

REPORT RequestId: 36db9855-74cf-4c3c-a560-c1baae94d96a Duration: 3.89 ms

As you can see, now we drop AWS Cache Latency from over 150ms to less than 4ms.

Build

make build

Deploy

make deploy

Cleanup

make delete