MerLoc Java

This project provides GateKeeper and local AWS Lambda Runtime components for Java runtime to be able to use MerLoc as live AWS Lambda development tool.

Note that, to be able to use MerLoc for Java runtime, first you need to setup MerLoc platform into your AWS account as explained at MerLoc Github page here.

1. Versioning

Artifact versions are in X.Y.Z format

X: Major version number.
- Increases only when there are big API and/or architectural changes.
- Breaks backward compatibility.
Y: Minor version number.
- Increases for small API changes and big improvements.
- Breaks backward compatibility.
Z: Patch version number.
- Increases for bug fixes and small improvements.
- Doesn’t break backward compatibility.

2. Requirements

JDK 1.8+ (for build and execution)
Maven 3.x (for build)

3. Build

To build:

$ git clone git@github.com:thundra-io/merloc-java.git
$ cd merloc-java/
$ mvn clean install

4. Setup

4.1. GateKeeper Setup

Add MerLoc GateKeeper layer: arn:aws:lambda:${region}:269863060030:layer:merloc-java:${version}

You can use the latest layer version (shown below) instead of the ${version} above:

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Note that the region of the ARN is dynamic, so you need to change it accordingly to the region where you deploy your function. So let’s say that you deploy your Lambda function to the Oregon (us-west-2) region. So the layer ARN will be: arn:aws:lambda:us-west-2:269863060030:layer:merloc-java:${version}
You need to switch the handler so MerLoc GateKeeper will wrap your original handler.

Java 8 on Amazon Linux 1:
- Set the handler to io.thundra.merloc.aws.lambda.gatekeeper.handler.GateKeeperLambdaHandler
- And then set the MERLOC_AWS_LAMBDA_HANDLER environment variable value to your original handler.
Java 8 on Amazon Linux 2 and Java 11 Corretto:
- Set AWS_LAMBDA_EXEC_WRAPPER environment variable to /opt/merloc_wrapper
Set MERLOC_BROKER_URL environment variable to the
- value of the merloc-broker.merlocbrokerwsapistageurl property which you get from AWS CDK broker setup output as shown in the example below:
- or value of the merlocbrokerwsapistageurl property which you get from AWS CloudFormation broker setup output as shown in the example below:

4.2. AWS Lambda Runtime Setup

Download MerLoc AWS Lambda embedded runtime from https://repo1.maven.org/maven2/io/thundra/merloc/merloc-aws-lambda-runtime-embedded/${version}/merloc-aws-lambda-runtime-embedded-${version}.jar

You can use the latest version (shown below) instead of the ${version} above:

4.2.1. IntelliJ IDEA

Right click on the project and click Open Module Settings.
Click Global Libraries and then click Java to add a new global library.
Select the MerLoc AWS Lambda runtime jar from the place where you downloaded above. And then chose the modules (single or multiple modules) in which Lambda handlers are located.

After these steps are completed, we have added MerLoc AWS Lambda runtime jar into the classpath of selected modules in which your AWS Lambda handlers exist.

Click Add Configuration and add a new Application configuration.
Select the JDK module (java 11 in the following example) and classpath module (hello-api module in the following example). Then set Main class to io.thundra.merloc.aws.lambda.runtime.embedded.LambdaRuntime.
Set MERLOC_BROKER_URL environment variable (likewise you did for GateKeeper above) to the
- value of the merloc-broker.merlocbrokerwsapistageurl property which you get from AWS CDK broker setup output as shown in the example below:
- or value of the merlocbrokerwsapistageurl property which you get from AWS CloudFormation broker setup output as shown in the example below:

4.2.2. Eclipse

Open Run Configurations.
Right click on Java Application and select New Configuration.
Select the project (hello-api in the following example). Then set Main class to io.thundra.merloc.aws.lambda.runtime.embedded.LambdaRuntime and click Apply.
Click Dependencies tab, select Classpath Entries, click Add External JARs and then select the MerLoc AWS Lambda runtime jar from the place where you downloaded above.

After these steps are completed, we have added MerLoc AWS Lambda runtime jar into the classpath of selected project in which your AWS Lambda handler(s) exist.

Set MERLOC_BROKER_URL environment variable (likewise you did for GateKeeper above) to the
- value of the merloc-broker.merlocbrokerwsapistageurl property which you get from AWS CDK broker setup output as shown in the example below:
- or value of the merlocbrokerwsapistageurl property which you get from AWS CloudFormation broker setup output as shown in the example below:

5. How to Use

5.1. IntelliJ IDEA

5.1.1. Run

Click Run to start MerLoc AWS Lambda Runtime.
So you will see MerLoc banner in the console.
Later on, trigger the AWS Lambda function. Then, the real request will be forwarded to MerLoc AWS Lambda Runtime on your local through MerLoc GateKeeper. So it will be executed locally and response will be returned to MerLoc GateKeeper and so to AWS Lambda function caller from there.

5.1.2. Debug

Click Debug to start MerLoc AWS Lambda Runtime in debug mode.
So you will see MerLoc banner in the console.
Put breakpoint from your IDE.
Then, trigger the AWS Lambda function. So the forwarded request will stop at the breakpoint you put on your local and you can debug AWS Lambda function locally.

5.1.3. Hot-Reload

While running MerLoc AWS Lambda Runtime on your local, apply your changes in the source code(s). Then go to Build in the menu bar and click Build Module to re-build module in which you updated source code(s).
After that you will see MerLoc log messages in your console which says that related function environment(s) (affected by changes) have been reloaded.
Then, trigger your AWS Lambda function again, and you will see that your changes are live in the running function on your local.

5.2. Eclipse

5.2.1. Run

Open Run Configurations. Select the configuration you created before during setup and click Run.
So you will see MerLoc banner in the console.
Later on, trigger the AWS Lambda function. Then, the real request will be forwarded to MerLoc AWS Lambda Runtime on your local through MerLoc GateKeeper. So it will be executed locally and response will be returned to MerLoc GateKeeper and so to AWS Lambda function caller from there.

5.2.2. Debug

Open Debug Configurations. Select the configuration you created before during setup and click Debug.
So you will see MerLoc banner in the console.
Put breakpoint from your IDE.
Then, trigger the AWS Lambda function. So the forwarded request will stop at the breakpoint you put on your local and you can debug AWS Lambda function locally.

5.2.3. Hot-Reload

TBD

6. Configuration

6.1. GateKeeper Configuration

MERLOC_BROKER_URL: This configuration is MANDATORY. You need to set this environment variable by broker URL as mentioned in the GateKeeper Setup section.
MERLOC_ENABLE: This configuration is OPTIONAL. Even though MerLoc GateKeeper layer is added and configured, you can disable it by setting the MERLOC_ENABLE environment variable to false. For example,
```
MERLOC_ENABLE=false
```
MERLOC_DEBUG_ENABLE: This configuration is OPTIONAL. By default, internal debug logs are disabled, but you can enable it by setting the MERLOC_DEBUG_ENABLE environment variable to true. For example,
```
MERLOC_DEBUG_ENABLE=true
```
MERLOC_BROKER_CONNECTION_NAME: This configuration is OPTIONAL. By default, the name of the connection to the broker is the name of the AWS Lambda function for GateKeeper. But you can change it by setting the MERLOC_BROKER_CONNECTION_NAME environment variable. For example,
```
MERLOC_BROKER_CONNECTION_NAME=serkan-connection
```
MERLOC_CLIENT_ACCESS_INTERVAL_ON_FAILURE: This configuration is OPTIONAL. By default, MerLoc GateKeeper tries to access to the client (your local AWS Lambda runtime) at every request even though the local runtime/function is not up/running or unreachable at the previous attempt. If it fails (local runtime is not up, rejected because of concurrency mode, etc ...), it bypasses MerLoc flow and forwards the request to your original handler for allowing the function to be executed as is. But such checks at every request introduce some additional little delays (up to 1 sec) if your function is configured to use MerLoc (and it is not disabled) and your local is not up. To get rid of such additional minor delay (when you are not running MerLoc on your local, and you didn't disable it), you can configure MERLOC_CLIENT_ACCESS_INTERVAL_ON_FAILURE environment variable to specify the client (your local AWS Lambda runtime) access check interval in seconds instead of at every request. So if a client (your local AWS Lambda runtime) access check fails, MerLoc GateKeeper will not check until the configured seconds have passed since the last failed check. For example (check every 5 minutes instead of at every request in case of failure),
```
MERLOC_CLIENT_ACCESS_INTERVAL_ON_FAILURE=300
```

6.2. AWS Lambda Runtime Configuration

MERLOC_BROKER_URL: This configuration is MANDATORY. You need to set this environment variable by broker URL as mentioned in the AWS Lambda Runtime Setup section.
MERLOC_AWS_LAMBDA_RUNTIME_CONCURRENCY_MODE: This configuration is OPTIONAL. Configures concurrency level at runtime level globally. Valid values are:
- REJECT: Rejects any invocation from any function if local runtime is busy executing other invocation. In this case, GateKeeper is informed by local runtime with the rejection and then GateKeeper forwards the request to the original user handler.
- WAIT: Waits any invocation from any function until runtime is available if local runtime is busy executing another invocation.
- PER_FUNCTION: Disables global lock between functions and runtime lock is handled at per function basis according to MERLOC_AWS_LAMBDA_RUNTIME_FUNCTION_CONCURRENCY_MODE configuration mentioned below. The default value is REJECT. For example,
```
MERLOC_AWS_LAMBDA_RUNTIME_CONCURRENCY_MODE=PER_FUNCTION
```
MERLOC_AWS_LAMBDA_RUNTIME_FUNCTION_CONCURRENCY_MODE: This configuration is OPTIONAL. Configures concurrency level at function level so executing a function doesn't block executing another function. Valid values are:
- REJECT: Rejects an invocation from a function if local runtime is busy executing other invocation of that function. In this case, GateKeeper is informed by local runtime with the rejection and then GateKeeper forwards the request to the original user handler.
- WAIT: Waits an invocation from a function until runtime is available if local runtime is busy executing another invocation of that function. The default value is REJECT. For example,
```
MERLOC_AWS_LAMBDA_RUNTIME_FUNCTION_CONCURRENCY_MODE=WAIT
```
MERLOC_DEBUG_ENABLE: This configuration is OPTIONAL. By default, internal debug logs are disabled, but you can enable it by setting the MERLOC_DEBUG_ENABLE environment variable to true. For example,
```
MERLOC_DEBUG_ENABLE=true
```
MERLOC_BROKER_CONNECTION_NAME: This configuration is OPTIONAL. By default, the name of the connection to the broker is default for local AWS Lambda runtime. Local AWS Lambda runtime connection with name default matches with all GateKeeper connections if there is no another local AWS Lambda runtime connection with the function name (or connection name set by MERLOC_BROKER_CONNECTION_NAME at GateKeeper) specifically. But you can change it by setting the MERLOC_BROKER_CONNECTION_NAME environment variable. For example,
```
MERLOC_BROKER_CONNECTION_NAME=serkan-connection
```

7. Limitations

If the resources (AWS RDS, AWS OpenSearch/Elasticsearch, AWS ElastiCache, etc ...) you are accessing inside the function are deployed inside a VPC, your local needs to have access to resources in the VPC. So you need to setup a VPN connection from your local machine to the VPC network. You can check this AWS blog post to learn how to do that.
Currently, AWS Lambda layers are not supported. So if you use layers, they will not be available on your local while running function locally as MerLoc doesn't download and extract layers onto your local environment.

8. Issues and Feedback

Please use GitHub Issues for any bug report, feature request and support.

9. Contribution

If you would like to contribute, please

Fork the repository on GitHub and clone your fork.
Create a branch for your changes and make your changes on it.
Send a pull request by explaining clearly what is your contribution.

Tip: Please check the existing pull requests for similar contributions and consider submit an issue to discuss the proposed feature before writing code.

10. License

Licensed under Apache License 2.0.