AWS Lambda is a neat service. And it got neater with the launch of external extensions, which allow you to have background processes that can continue running (e.g. for cleanup) after a Lambda function has returned its response. But sometimes you want to do cleanup in the function process itself. Here's a library to achieve that.
First, create a Lambda function. You need to include the supporting postinvoke
external extension in a layer. Here's an example that you can use (uncomment
as appropriate for your architecture):
Transform: AWS::Serverless-2016-10-31
Resources:
Example:
Type: AWS::Serverless::Function
Properties:
CodeUri: ./example/bootstrap
Runtime: provided.al2
Handler: unused
Timeout: 30
MemorySize: 512
Architectures: [arm64]
Layers:
- !Sub arn:aws:lambda:${AWS::Region}:514202201242:layer:postinvoke-arm64:1
# Architectures: [x86_64]
# Layers:
# - !Sub arn:aws:lambda:${AWS::Region}:514202201242:layer:postinvoke-x86_64:1Second, here's the code for an example Lambda function:
package main
import (
"context"
"encoding/json"
"fmt"
"github.com/aidansteele/postinvoke"
"github.com/aws/aws-lambda-go/lambda"
"time"
)
func main() {
postinvoke.Shutdown(func() {
// this will be executed when the lambda environment shuts down.
// you get 300ms to clean up - be quick!
fmt.Println("bye y'all!")
})
h := lambda.NewHandler(handle)
h = postinvoke.WrapHandler(h, nil) // don't forget this line
lambda.StartHandler(h)
}
func handle(ctx context.Context, input json.RawMessage) (json.RawMessage, error) {
// this is where you do your lambda thing
fmt.Println(string(input))
postinvoke.Run(ctx, func() {
// and here is where you can do your post-invoke cleanup. this code runs
// after the lambda function has returned its response to the caller
fmt.Println("first on stack")
})
postinvoke.Run(ctx, func() {
// you can have multiple post-invoke methods
// executed sequentially, in a defer-like stack
fmt.Println("second on stack")
time.Sleep(3 * time.Second)
fmt.Println("second on complete")
})
return input, nil
}This is what is logged by the above Lambda function. Note from the timestamps that the environment is shut down about six minutes later.
