awscli - lambda function update trigger

Perform the following steps-

1. Check the versions of lambda first by running the following cli command. And the Fetch the FunctionARN of the latest version.

aws lambda list-versions-by-function --function-name LAMBDA_NAME

2. Get the cloudfront distribution json data first by the following command.

aws cloudfront get-distribution-config --id DISTRIBUTION_ID > cf_config.json

3. Create a file named updated_cf_config.json by fetching DistributionConfig key from the cf_config.json.

4. Now Put the FunctionARN of the latest Version of lambda inside the "LambdaFunctionAssociations" -> "LambdaFunctionARN"

5. Update cloudfront distribution by running the command. To update the cloudfront distribution we need ETAG from cf_config.json:

aws cloudfront update-distribution --distribution-config file://cf_config.json --id DISTRIBUTION_ID --if-match ETAG

Should anyone stumble upon this, I created a simple Node.js script to handle the CloudFront update.

It requires you capture the response of the aws lambda publish-version command into lambda_publish_response.json, and that you change the cloudFrontDistributionId variable, but everything else "should just work":

const fs = require('fs');
const {exec} = require('child_process');

const cloudFrontDistributionId = 'EXXXXXXXXXXXXX';
const currentCloudFrontConfigFile = 'cf_config.json';
const updatedCloudFrontConfigFile = 'cf_config_updated.json';
const lambdaPublishResponseFile = 'lambda_publish_response.json';

exec(`aws cloudfront get-distribution-config --id ${cloudFrontDistributionId} > ${currentCloudFrontConfigFile}`, (error, stdout, stderr) => {
    if (error) {
        console.error(`error: ${error.message}`);

        return process.exit(1);
    }

    if (stderr) {
        console.error(`stderr: ${stderr}`);

        return process.exit(1);
    }

    if (!fs.existsSync(lambdaPublishResponseFile)) {
        console.error('Run this first: `aws lambda publish-version --function-name LambdaFunctionName > lambda_publish_response.json`');

        return process.exit(1);
    }

    let cfConfig = JSON.parse(fs.readFileSync(currentCloudFrontConfigFile));
    const etag = cfConfig.ETag;
    const lambdaPublishData = JSON.parse(fs.readFileSync(lambdaPublishResponseFile));

    cfConfig.DistributionConfig.DefaultCacheBehavior.LambdaFunctionAssociations.Items[0].LambdaFunctionARN = lambdaPublishData.FunctionArn;

    fs.writeFileSync(updatedCloudFrontConfigFile, JSON.stringify(cfConfig.DistributionConfig));

    exec(`aws cloudfront update-distribution --distribution-config file://${updatedCloudFrontConfigFile} --id ${cloudFrontDistributionId} --if-match ${etag}`, (error, stdout, stderr) => {
        if (error) {
            return console.error(`error: ${error.message}`);
        }

        if (stderr) {
            return console.error(`stderr: ${stderr}`);
        }

        console.log(`stdout: ${stdout}`);

        fs.unlinkSync(lambdaPublishResponseFile);
        fs.unlinkSync(currentCloudFrontConfigFile);
        fs.unlinkSync(updatedCloudFrontConfigFile);
    });
});

Here is a Gist listing all the commands required to make this happen: https://gist.github.com/neonexus/3062b34b09896fa027e22d332dd65069