poc java lambda writing to s3 file

instructions.md

Upload base64 encoded file to S3

1. Encrypt the .env file locally (on linux / mac):

   base64 your-env-file.env > encrypted-env-file.env

2. Upload the encrypted-env-file.env to S3 (via aws-cli)

Notes for Production

1. IAM Role: Ensure the Lambda execution role has the s3:GetObject permission for the specific S3 bucket and file.
2. Error Handling: Add better error handling for cases where the S3 object is unavailable.
3. Testing: Test locally using AWS SAM or deploy the Lambda and test via API Gateway/CloudWatch logs.

java_lambda_serverless_handler.java

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

import java.util.Base64;
import java.util.concurrent.TimeUnit;

// AWS Lambda Handler
public class FeatureFlagHandler implements RequestHandler<Object, String> {

    private static final String BUCKET_NAME = "your-s3-bucket";
    private static final String FILE_KEY = "path/to/your/envfile.env";
    private static final Cache<String, String> cache;

    private final AmazonS3 s3Client;

    static {
        // Initialize cache with 30-second expiry
        cache = CacheBuilder.newBuilder()
                .expireAfterWrite(30, TimeUnit.SECONDS)
                .build();
    }

    public FeatureFlagHandler() {
        // Initialize S3 client
        this.s3Client = AmazonS3ClientBuilder.defaultClient();
    }

    @Override
    public String handleRequest(Object input, Context context) {
        try {
            return cache.get("featureFlags", this::fetchAndDecodeFeatureFlags);
        } catch (Exception e) {
            context.getLogger().log("Error fetching feature flags: " + e.getMessage());
            return null;
        }
    }

    // Fetch and decode feature flags from S3
    private String fetchAndDecodeFeatureFlags() {
        String encryptedData = s3Client.getObjectAsString(BUCKET_NAME, FILE_KEY);
        return new String(Base64.getDecoder().decode(encryptedData));
    }
}