# lambda-promtail

This is a sample deployment for lambda-promtail - Below is a brief explanation of what we have generated for you:

```bash
.
├── Makefile                    <-- Make to automate build
├── Dockerfile                  <-- Uses the AWS Lambda Go base image
├── README.md                   <-- This instructions file
├── lambda-promtail             <-- Source code for a lambda function
│   └── main.go                 <-- Lambda function code
```

## Requirements

* AWS CLI already configured with Administrator permission
* [Terraform](https://www.terraform.io/downloads.html)

If you want to modify the lambda-promtail code you will also need: 
* [Docker installed](https://www.docker.com/community-edition)
* [Golang](https://golang.org)

## Setup process

### Building and Packaging

The provided Makefile has targets `build`, and `clean`.

`build` builds the lambda-promtail as a Go static binary. To build the container image properly you should run `docker build . -f tools/lambda-promtail/Dockerfile` from the root of the Loki repository,you can upload this image to your AWS ECR and use via Lambda. `clean` will remove the built Go binary.

### Packaging and deployment

The easiest way to deploy to AWS Lambda using the Golang runtime is to use the `lambda-promtail` image by uploading it to your ECR.

Alternatively you can build the Go binary and upload it to Lambda as a zip:
```bash
GOOS=linux CGO_ENABLED=0 go build main.go
zip function.zip main
```

To deploy your application for the first time, first make sure you've set the following value in the Terraform file:
- `WRITE_ADDRESS`

This is the [Loki Write API](https://grafana.com/docs/loki/latest/api/#post-lokiapiv1push) compatible endpoint that you want to write logs to, either promtail or Loki.

The `lambda-promtail` code picks this value up via an environment variable.

Also, if your deployment requires a [VPC configuration](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lambda_function#vpc_config), make sure to edit the `vpc_config` field in `main.tf` manually. Additonal documentation for the Lambda specific Terraform configuration is [here](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lambda_function#vpc_config).

Then use Terraform to deploy:

```bash
terraform apply -var "<ecr-repo>:<tag>" -var "write_address=https://your-loki-url/loki/api/v1/push" -var "password=<basic-auth-pw>" -var "username=<basic-auth-username>" -var 'log_group_names=["log-group-01", "log-group-02"]' -var 'extra_labels="name1,value1,name2,value2"' -var "tenant_id=<value>"
```

or CloudFormation:

```bash
aws cloudformation create-stack --stack-name lambda-promtail-stack --template-body file://template.yaml --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM --region us-east-2 --parameters ParameterKey=WriteAddress,ParameterValue=https://your-loki-url/loki/api/v1/push ParameterKey=Username,ParameterValue=<basic-auth-username> ParameterKey=Password,ParameterValue=<basic-auth-pw> ParameterKey=LambdaPromtailImage,ParameterValue=<ecr-repo>:<tag> ParameterKey=ExtraLabels,ParameterValue="name1,value1,name2,value2" ParameterKey=TenantID,ParameterValue=<value>
```

# Appendix

## Golang installation

Please ensure Go 1.x (where 'x' is the latest version) is installed as per the instructions on the official golang website: https://golang.org/doc/install

For example:

```bash
GO_VERSION=go1.16.6.linux-amd64.tar.gz

rm -rf /usr/local/bin/go*
rm -rf /usr/local/go
curl -O https://storage.googleapis.com/golang/$GO_VERSION
tar -zxvf $GO_VERSION
sudo mv go /usr/local/
rm $GO_VERSION
ln -s /usr/local/go/bin/* /usr/local/bin/
```

A quickstart way would be to use Homebrew, chocolatey or your Linux package manager.

#### Homebrew (Mac)

Issue the following command from the terminal:

```shell
brew install golang
```

If it's already installed, run the following command to ensure it's the latest version:

```shell
brew update
brew upgrade golang
```

#### Chocolatey (Windows)

Issue the following command from the powershell:

```shell
choco install golang
```

If it's already installed, run the following command to ensure it's the latest version:

```shell
choco upgrade golang
```

## Limitations
- Error handling: If promtail is unresponsive, `lambda-promtail` will drop logs after `retry_count`, which defaults to 2.
- AWS CloudWatch [quotas](https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/cloudwatch_limits_cwl.html) state that the event size is limited to 256kb. `256 KB (maximum). This quota can't be changed.`