Composer vs Docker: What are the differences?
Composer: Dependency Manager for PHP. Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you; Docker: Enterprise Container Platform for High-Velocity Innovation. The Docker Platform is the industry-leading container platform for continuous, high-velocity innovation, enabling organizations to seamlessly build and share any application — from legacy to what comes next — and securely run them anywhere.
Composer can be classified as a tool in the "Package Managers" category, while Docker is grouped under "Virtual Machine Platforms & Containers".
"Must have dependency manager for PHP" is the primary reason why developers consider Composer over the competitors, whereas "Rapid integration and build up" was stated as the key factor in picking Docker.
Composer and Docker are both open source tools. Docker with 54K GitHub stars and 15.6K forks on GitHub appears to be more popular than Composer with 20.2K GitHub stars and 5.54K GitHub forks.
Spotify, Pinterest, and Twitter are some of the popular companies that use Docker, whereas Composer is used by Walls.io, Zumba, and Infoshare. Docker has a broader approval, being mentioned in 3527 company stacks & 3449 developers stacks; compared to Composer, which is listed in 95 company stacks and 55 developer stacks.
lxd/lxc and Docker aren't congruent so this comparison needs a more detailed look; but in short I can say: the lxd-integrated administration of storage including zfs with its snapshot capabilities as well as the system container (multi-process) approach of lxc vs. the limited single-process container approach of Docker is the main reason I chose lxd over Docker.