GitLab CI/CD
GitLab CI/CD is a tool built into GitLab for software development through the continuous methodologies:
Continuous Integration (CI)
Continuous Delivery (CD)
Continuous Deployment (CD)
GitLab Runner
GitLab Runner is an application that works with GitLab CI/CD to run jobs in a pipeline.
Executors
GitLab Runner implements a number of executors that can be used to run your builds in different scenarios.
Registering runners
Registering a runner is the process that binds the runner with a GitLab instance.
操作流程概述
如何使用 GitLab CI/CD 进行 CI/CD 操作（这里只复述大致流程）？
1）前期设置（需要管理权限）：
执行 gitlab-runner register 以向 gitlab 注册 executor 实例（可以注册各种 executor 类型）
2）开发使用：
当提交后，将触发作业，开始执行流水线；
如下是对上述流程的补充说明，用于辅助我们理解 GitLab CI/CD 是什么：
1）对于 .gitlab.yml 文件，其内容多是 Shell 脚本，以及定义脚本的执行流程和执行条件等等；
2）可以向 gitlab 注册多个 executor 实例：SSH Executor 将在远程主机中执行命令；Docker Executor 将在容器中执行命令；
3）术语 gitlab-runner 与 executor 经常会被混淆；
参考文献
Executors | GitLab
GitLab Runner | GitLab
Registering runners | GitLab