The cuckoo egg testing lambda
Oh, there is an error in my Lambda function. But - what is the event JSON input which caused the error? Oh, I forgot to log the event in my Lambda code. Damned! It would be great to swap the code with a “just dump the event code” and slip it like a cuckoo egg. Afterwards, get the event and restore the old Lambda!
No problem!
Swap
Only some people know that you can also download the function code of a Lambda function. This can be done via the Code.Location property in the get-function API call. This property contains a presigned URL to download the function code.
That means we could save the old function code and swap it with the test “cuckoo egg” function code. Then we store the event and restore the function afterwards.
You could also use this pattern to replace Lambda functions in a distributed system with mock Functions, which respond with a fixed value.
Walkthrough
These are the steps:
- Save old Lambda, download code
aws lambda get-function
--function-name "{{.NAME}}"
--query 'Code.Location'
--output text >download.txt
wget -i download.txt -O {{.CODE}}
You must also store the Function Name, the Runtime and the handler. The language and the handler will often be the same as in your other Lambda Functions.
- Deploy egg
aws lambda update-function-configuration --runtime go1.x --function-name {{.NAME}} --handler main
aws lambda update-function-code --function-name {{.NAME}} --zip-file fileb://./dist/main.zip
The function for the event is of course written in GO. Should be easy to port to other languages.
-
Create event, get data from CloudWatch logs
-
Restore old code:
aws lambda update-function-configuration --runtime {{.RUNTIME}} --function-name {{.NAME}} --handler {{.HANDLER}}
aws lambda update-function-code --function-name {{.NAME}} --zip-file fileb://{{.CODE}}
All steps are coded in the Taskfile.yml file.
See the Repo on github
Usage with taskfile.dev
See Taskfile.yaml
A) Get code from github
B) Update the Taskfile.yml with your values:
NAME: polly-notes-api-searchFunction
RUNTIME: python3.8
HANDLER: app.lambda_handler
CODE: code.zip
These are example values.
- Save:
task save - Deploy:
task deploy - Invoke Lambda with event
- Restore:
task restore
Save
task save
task: [save] aws lambda get-function --function-name "polly-notes-api-searchFunction" --query 'Code.Location' --output text >download.txt
task: [save] wget -i download.txt -O code.zip
--2023-06-19 18:07:27-- https://awslambda-eu-cent-1-tasks.s3.eu-central-1.amazonaws.com/snapshots/139008737997/polly-notes-api-searchFunction-***
&X-Amz-Credential=ASIAZ***%2Feu-central-1%2Fs3%2Faws4_request
&X-Amz-Signature=00***7
Auflösen des Hostnamens awslambda-eu-cent-1-tasks.s3.eu-central-1.amazonaws.com (awslambda-eu-cent-1-tasks.s3.eu-central-1.amazonaws.com)… 52.219.171.254
Verbindungsaufbau zu awslambda-eu-cent-1-tasks.s3.eu-central-1.amazonaws.com (awslambda-eu-cent-1-tasks.s3.eu-central-1.amazonaws.com)|52.219.171.254|:443 … verbunden.
HTTP-Anforderung gesendet, auf Antwort wird gewartet … 200 OK
Länge: 12042877 (11M) [application/zip]
Wird in »code.zip« gespeichert.
code.zip 100%[========================================================================================>] 11,48M 23,9MB/s in 0,5s
2023-06-19 18:07:28 (23,9 MB/s) - »code.zip« gespeichert [12042877/12042877]
BEENDET --2023-06-19 18:07:28--
Verstrichene Zeit: 1,0s
Geholt: 1 Dateien, 11M in 0,5s (23,9 MB/s)
Deploy
task deploy
updating: main (deflated 58%)
task: [deploy] aws lambda update-function-configuration --runtime go1.x --function-name polly-notes-api-searchFunction --handler main
{
"FunctionName": "polly-notes-api-searchFunction",
...
"Runtime": "go1.x",
...
}
task: [deploy] aws lambda update-function-code --function-name polly-notes-api-searchFunction --zip-file fileb://./dist/main.zip
{
"FunctionName": "polly-notes-api-searchFunction",
"Runtime": "go1.x",
"Handler": "main",
"CodeSize": 2691074,
...
"PackageType": "Zip",
...
}
Restore
task restore
task: [restore] aws lambda update-function-configuration --runtime python3.8 --function-name polly-notes-api-searchFunction --handler app.lambda_handler
{
"FunctionName": "polly-notes-api-searchFunction",
...
"Runtime": "python3.8",
...
"Handler": "app.lambda_handler",
...
}
task: [restore] aws lambda update-function-code --function-name polly-notes-api-searchFunction-GdFQpjWz1XKZ --zip-file fileb://code.zip
{
"FunctionName": "polly-notes-api-searchFunction",
...
"Runtime": "python3.8",
...
"Handler": "app.lambda_handler",
"CodeSize": 12042877,
...
}
Conclusion
With this little trick, you can inject test code into a running Lambda based microservice system and restore the old environment afterwards.
Happy building!
If you need consulting for your serverless project, don’t hesitate to get in touch with the sponsor of this blog, tecRacer.
For more AWS development stuff, follow me on dev https://dev.to/megaproaktiv. Want to learn GO on AWS? GO here
