If you google "matrix from hell", you'll see many articles about how Docker solves the matrix from hell. So what is the matrix from hell? Put simply, it is the challenge of packaging any application, regardless of language/frameworks/dependencies, so that it can run on any cloud, regardless of operating systems/hardware/infrastructure.
The original matrix from hell: applications were tightly coupled with underlying hardware
Docker solved for the matrix from hell by decoupling the application from the underlying operating system and hardware. It did this by packaging all dependencies inside Docker containers, including the OS. This makes Docker containers "portable", i,e, they can run on any cloud or machine without the dreaded "it works on this machine" problems. This is the single biggest reason Docker is considered the hottest new technology of the last decade.
With DevOps principles gaining center stage over the last few years, Ops teams have started automating their tasks like provisioning infrastructure, managing config, triggering production deployments, etc. IT automation tools like Ansible and Terraform help tremendously with these use cases since they allow you to represent your infrastructure-as-code, which can be versioned and committed to source control. Most of these tools are configured with a YAML or JSON based language which describes the activity you're trying to achieve.