CI/CD 解決方案都是基於 docker 嗎？

Bitbucket Pipelines

Pipelines can build and test anything that can run on Linux as we run your builds in Docker containers.

Jenkins

Jenkins 支持各种运行方式，可通过系统包、Docker 或者通过一个独立的 Java 程序。

Travis CI

Travis CI builds can run and build Docker images, and can also push images to Docker repositories or other remote storage.

circleci

This example adds a job called build that spins up a container running a pre-built CircleCI Docker image for Node.

結論

CI/CD 解決方案可能支援多種不同的運行環境，一定會支援 docker，但不只是 docker。