slack-slash-lambda

This repo holds code and configuration to create a lambda based slash commands for Slack. The processing of the commands is done asynchronously.

Details for geeks

Slack allows support both sync and async API. For synchronus calls the timeout is 3 seconds. For longer processing periods, async API is the way to go. This repository configured to respond in async manner. It is done by responding with 200 OK to the initial call and passing the callback url to the handler function.

Pre-Requirements

To deploy this you will need the following

1. AWS credentails and access to create Cloudformation stacks, Lambda functions, Api Gateways, IAM policies and S3 buckets
2. S3 bucket
3. awscli
4. aws-sam-cli
5. Access in Slack to create your own App

Secrets

Secrets are passed to the lambda via environment variables. These are set by CloudFormation via parameters. Add secrets to envars.sample.json file and rename it to envars.json.

The keys:

• SESSIONISE_KEY: the API id you can generate in sessionize.com under API/Embed section
• TITO_KEY: v3 API key generated in the user profile
• SLACK_KEY: Slack's app signing secret key generated in the App credentails section

Local testing

Testing behaviour of the lambda can be done locally:

$ sam local invoke -n envars.json -e event_cfp.json

sam local start-api won't work because currently local API Gateway doesn't support mapping templates.

Build and Deploy

First build and package:

$ sam build
$ sam package --s3-bucket <bucket> --output-template-file packaged.yaml

Now deploy with awscli:

$ cloudformation deploy --template-file packaged.yaml --stack-name <name> --capabilities CAPABILITY_IAM --parameter-overrides $(jq -r '.Function | to_entries | .[] | .key +"="+ .value ' envars.json)

If deployed successfully, you can list outputs with:

$ aws cloudformation describe-stacks --stack-name <name> --query "Stacks[0].Outputs"

Configuring Slack

Create a new App in Slack. Under the Slash Command section add your commands. Set Request URL to point at the OutputValue of Api OutputKey.