Add Jenkins quick reference page

doc/ci/README.md

@@ -53,6 +53,9 @@ the following documents:
 - [GitLab CI/CD basic workflow](introduction/index.md#basic-cicd-workflow).
 - [Step-by-step guide for writing `.gitlab-ci.yml` for the first time](../user/project/pages/getting_started_part_four.md).
 
+If you're coming over from Jenkins, you can also check out our handy [reference](jenkins/index.md)
+for converting your pipelines.
+
 You can also get started by using one of the
 [`.gitlab-ci.yml` templates](https://gitlab.com/gitlab-org/gitlab-ce/tree/master/lib/gitlab/ci/templates)
 available through the UI. You can use them by creating a new file,

doc/ci/jenkins/index.md

@@ -0,0 +1,204 @@
+---
+comments: false
+type: index, howto
+---
+
+# Migrating from Jenkins
+
+A lot of GitLab users have successfully migrated to GitLab CI/CD from Jenkins. To make this
+easier if you're just getting started, we've collected several resources here that you might find useful
+before diving in.
+
+First of all, our [Quick Start Guide](../quick_start/README.md) contains a good overview of how GitLab CI/CD works.
+You may also be interested in [Auto DevOps](../../topics/autodevops/index.md) which can potentially be used to build, test,
+and deploy your applications with little to no configuration needed at all.
+
+Otherwise, read on for important information that will help you get the ball rolling. Welcome
+to GitLab!
+
+## Important differences
+
+There are some high level differences between the products worth mentioning:
+
+- With GitLab you don't need a root `pipeline` keyword to wrap everything.
+- All jobs within a single stage always run in parallel, and all stages run in sequence. We are planning
+  to allow certain jobs to break this sequencing as needed with our [directed acyclic graph](https://gitlab.com/gitlab-org/gitlab-ce/issues/47063)
+  feature.
+- The `.gitlab-ci.yml` file is checked in to the root of your repository, much like a Jenkinsfile, but
+  is in the YAML format (see [complete reference](../yaml/README.md)) instead of a Groovy DSL. It's most
+  analagous to the declarative Jenkinsfile format.
+- GitLab comes with a [container registry](../../user/project/container_registry.md), and we recommend using
+  container images to set up your build environment.
+
+## Artifact publishing
+
+Artifacts may work a bit differently than you've used them with Jenkins. In GitLab, any job can define
+a set of artifacts to be saved by using the `artifacts:` keyword. This can be configured to point to a file
+or set of files that can then be persisted from job to job. Read more on our detailed [artifacts documentation](../../user/project/pipelines/job_artifacts.html)
+
+```yaml
+pdf:
+  script: xelatex mycv.tex
+  artifacts:
+    paths:
+    - ./mycv.pdf
+    - ./output/
+    expire_in: 1 week
+```
+
+Additionally, we have package management features like a built-in container, NPM, and Maven registry that you
+can leverage. You can see the complete list of packaging features (which includes links to documentation)
+in the [Packaging section of our documentation](../../README.md#package).
+
+## Integrated features
+
+Where you may have used plugins to get things like code quality, unit tests, security scanning, and so on working in Jenkins,
+GitLab takes advantage of our connected ecosystem to automatically pull these kinds of results into
+your Merge Requests, pipeline details pages, and other locations. You may find that you actually don't
+need to configure anything to have these appear.
+
+If they aren't working as expected, or if you'd like to see what's available, our [CI feature index](../README.md#feature-set) has the full list
+of bundled features and links to the documentation for each.
+
+## Converting Declarative Jenkinsfiles
+
+Declarative Jenkinsfiles contain "Sections" and "Directives" which are used to control the behavior of your
+pipelines. There are equivalents for all of these in GitLab, which we've documented below.
+
+This section is based on the [Jenkinsfile syntax documentation](https://jenkins.io/doc/book/pipeline/syntax/)
+and is meant to be a mapping of concepts there to concepts in GitLab.
+
+### Sections
+
+#### `agent`
+
+The agent section is used to define how a pipeline will be executed. For GitLab, we use the [GitLab Runner](../runners/README.md)
+to provide this capability. You can configure your own runners in Kubernetes or on any host, or take advantage
+of our shared runner fleet (note that the shared runner fleet is only available for GitLab.com users.) The link above will bring you to the documenation which will describe how to get
+up and running quickly. We also support using [tags](../runners/README.md#using-tags) to direct different jobs
+to different Runners (execution agents).
+
+The `agent` section also allows you to define which Docker images should be used for execution, for which we use
+the [`image`](../yaml/README.md#image) keyword. The `image` can be set on a single job or at the top level, in which
+case it will apply to all jobs in the pipeline.
+
+```yaml
+my_job:
+  image: alpine
+  ...
+```
+
+#### `post`
+
+The `post` section defines the actions that should be performed at the end of the pipeline. GitLab also supports
+this through the use of stages. You can define your stages as follows, and any jobs assigned to the `before_pipeline`
+or `after_pipeline` stages will run as expected. You can call these stages anything you like.
+
+```yaml
+stages:
+  - before_pipeline
+  - build
+  - test
+  - deploy
+  - after_pipeline
+```  
+
+Setting a step to be performed before and after any job can be done via the [`before_script` and `after_script` keywords](../yaml/README.md#before_script-and-after_script).
+
+```yaml
+default:
+  before_script:
+    - echo "I run before any jobs starts in the entire pipeline, and can be responsible for setting up the environment."
+```
+
+#### `stages`
+
+GitLab CI also lets you define stages, but is a little bit more free-form to configure. The GitLab [`stages` keyword](../yaml/README.md#stages)
+is a top level setting that enumerates the list of stages, but you are not required to nest individual jobs underneath
+the `stages` section. Any job defined in the `.gitlab-ci.yml` can be made a part of any stage through use of the 
+[`stage:` keyword](../yaml/README.md#stage).
+
+Note that, unless otherwise specified, every pipeline is instantiated with a `build`, `test`, and `deploy` stage
+which are run in that order. Jobs that have no `stage` defined are placed by default in the `test` stage.
+Of course, each job that refers to a stage must refer to a stage that exists in the pipeline configuration.
+
+```yaml
+stages:
+  - build
+  - test
+  - deploy
+
+my_job:
+  stage: build
+  ...
+```
+
+#### `steps`
+
+The `steps` section is equivalent to the [`script` section](../yaml/README.md#script) of an individual job. This is
+a simple YAML array with each line representing an individual command to be run.
+
+```yaml
+my_job:
+  script:
+    - echo "hello! the current time is:"
+    - time
+  ...
+```
+
+### Directives
+
+#### `environment`
+
+In GitLab, we use the [`variables` keyword](../yaml/README.md#variables) to define different variables at runtime.
+These can also be set up through the GitLab UI, under CI/CD settings. See also our [general documentation on variables](../variables/README.md),
+including the section on [protected variables](../variables/README.md#protected-environment-variables) which can be used
+to limit access to certain variables to certain environments or runners.
+
+```yaml
+variables:
+  POSTGRES_USER: user
+  POSTGRES_PASSWORD: testing_password
+```
+
+#### `options`
+
+Here, options for different things exist associated with the object in question itself. For example, options related
+to jobs are defined in relation to the job itself. If you're looking for a certain option, you should be able to find
+where it's located by searching our [complete configuration reference](../yaml/README.md) page.
+
+#### `parameters`
+
+GitLab does not require you to define which variables you want to be available when starting a manual job. A user
+can provide any variables they like.
+
+#### `triggers` / `cron`
+
+Because GitLab is integrated tightly with git, SCM polling options for triggers are not needed. We support an easy to use
+[syntax for scheduling pipelines](../../user/project/pipelines/schedules.md).
+
+#### `tools`
+
+GitLab does not support a separate `tools` directive. Our best-practice reccomendation is to use pre-built
+container images, which can be cached, and can be built to already contain the tools you need for your pipelines. Pipelines can
+be set up to automatically build these images as needed and deploy them to the [container registry](../../user/project/container_registry.md).
+
+If you're not using container images with Docker/Kubernetes, for example on Mac or FreeBSD, then the `shell` executor does require you to
+set up your environment either in advance or as part of the jobs. You could create a `before_script`
+action that handles this for you.
+
+#### `input`
+
+Similar to the `parameters` keyword, this is not needed because a manual job can always be provided runtime
+variable entry.
+
+#### `when`
+
+GitLab does support a [`when` keyword](../yaml/README.md#when) which is used to indicate when a job should be
+run in case of (or despite) failure, but most of the logic for controlling pipelines can be found in
+our very powerful [`only/except` rules system](../yaml/README.md#onlyexcept-basic) (see also our [advanced syntax](../yaml/README.md#onlyexcept-basic))
+
+```yaml
+my_job:
+  only: branches
+```

doc/ci/quick_start/README.md

@@ -13,6 +13,10 @@ NOTE: **Note:**
 Please keep in mind that only project Maintainers and Admin users have
 the permissions to access a project's settings.
 
+NOTE: **Note:**
+Coming over to GitLab from Jenkins? Check out our [reference](../jenkins/index.md)
+for converting your pre-existing pipelines over to our format.
+
 GitLab offers a [continuous integration][ci] service. If you
 [add a `.gitlab-ci.yml` file][yaml] to the root directory of your repository,
 and configure your GitLab project to use a [Runner], then each commit or