In a 2015 AWS case study, Richard Crowley, Director of Operations said “with traditional IT, it would take weeks or months to contend with hardware lead times to add more capacity. Using AWS, we can look at user metrics weekly or daily and react with new capacity in 30 seconds.”

Slack needed to pick an infrastructure partner that could support the exponential growth they were experiencing. AWS is the cloud provider that supplied them with i2.xlarge Amazon Elastic Compute Cloud (Amazon EC2) instances for their LAMP stack, Amazon Simple Storage Service (Amazon S3) for user's file uploads and static assets, and ELB to Load Balance workloads across their EC2 instances.

For security, Slack went with Amazon Virtual Private Cloud (VPC) for controlling security groups and firewall rules and AWS Identity and Access Management (IAM) for controlling user credentials and roles.

In 2018, Slack signed an agreement with AWS to spend at least $50 million a year over five years, for a total of at least $250 million, according to the company’s filing with the SEC for a public stock listing (via CNBC)