Merge pull request #11746 from soltysh/job_controller_proposal

docs/proposals/job.md

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+<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
+
+If you are using a released version of Kubernetes, you should
+refer to the docs that go with that version.
+
+<strong>
+The latest 1.0.x release of this document can be found
+[here](http://releases.k8s.io/release-1.0/docs/proposals/job.md).
+
+Documentation for other releases can be found at
+[releases.k8s.io](http://releases.k8s.io).
+</strong>
+--
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+
+# Job Controller
+
+## Abstract
+
+A proposal for implementing a new controller - Job controller - which will be responsible
+for managing pod(s) that require running once to completion even if the machine
+the pod is running on fails, in contrast to what ReplicationController currently offers.
+
+Several existing issues and PRs were already created regarding that particular subject:
+* Job Controller [#1624](https://github.com/GoogleCloudPlatform/kubernetes/issues/1624)
+* New Job resource [#7380](https://github.com/GoogleCloudPlatform/kubernetes/pull/7380)
+
+
+## Use Cases
+
+1. Be able to start one or several pods tracked as a single entity.
+1. Be able to run batch-oriented workloads on Kubernetes.
+1. Be able to get the job status.
+1. Be able to specify the number of instances performing a job at any one time.
+1. Be able to specify the number of successfully finished instances required to finish a job.
+
+
+## Motivation
+
+Jobs are needed for executing multi-pod computation to completion; a good example
+here would be the ability to implement any type of batch oriented tasks.
+
+
+## Implementation
+
+Job controller is similar to replication controller in that they manage pods.
+This implies they will follow the same controller framework that replication
+controllers already defined.  The biggest difference between a `Job` and a
+`ReplicationController` object is the purpose; `ReplicationController`
+ensures that a specified number of Pods are running at any one time, whereas
+`Job` is responsible for keeping the desired number of Pods to a completion of
+a task.  This difference will be represented by the `RestartPolicy` which is
+required to always take value of `RestartPolicyNever` or `RestartOnFailure`.
+
+
+The new `Job` object will have the following content:
+
+```go
+// Job represents the configuration of a single job.
+type Job struct {
+    TypeMeta
+    ObjectMeta
+
+    // Spec is a structure defining the expected behavior of a job.
+    Spec JobSpec
+
+    // Status is a structure describing current status of a job.
+    Status JobStatus
+}
+
+// JobList is a collection of jobs.
+type JobList struct {
+    TypeMeta
+    ListMeta
+
+    Items []Job
+}
+```
+
+`JobSpec` structure is defined to contain all the information how the actual job execution
+will look like.
+
+```go
+// JobSpec describes how the job execution will look like.
+type JobSpec struct {
+
+    // Parallelism specifies the maximum desired number of pods the job should
+    // run at any given time. The actual number of pods running in steady state will
+    // be less than this number when ((.spec.completions - .status.successful) < .spec.parallelism),
+    // i.e. when the work left to do is less than max parallelism.
+    Parallelism *int
+
+    // Completions specifies the desired number of successfully finished pods the
+    // job should be run with. Defaults to 1.
+    Completions *int
+
+    // Selector is a label query over pods running a job.
+    Selector map[string]string
+
+    // Template is the object that describes the pod that will be created when
+    // executing a job.
+    Template *PodTemplateSpec
+}
+```
+
+`JobStatus` structure is defined to contain informations about pods executing
+specified job.  The structure holds information about pods currently executing
+the job.
+
+```go
+// JobStatus represents the current state of a Job.
+type JobStatus struct {
+    Conditions []JobCondition
+
+    // CreationTime represents time when the job was created
+    CreationTime util.Time
+
+    // StartTime represents time when the job was started
+    StartTime util.Time
+
+    // CompletionTime represents time when the job was completed
+    CompletionTime util.Time
+
+    // Active is the number of actively running pods.
+    Active int
+
+    // Successful is the number of pods successfully completed their job.
+    Successful int
+
+    // Unsuccessful is the number of pods failures, this applies only to jobs
+    // created with RestartPolicyNever, otherwise this value will always be 0.
+    Unsuccessful int
+}
+
+type JobConditionType string
+
+// These are valid conditions of a job.
+const (
+    // JobSucceeded means the job has successfully completed its execution.
+    JobSucceeded JobConditionType = "Complete"
+)
+
+// JobCondition describes current state of a job.
+type JobCondition struct {
+    Type               JobConditionType
+    Status             ConditionStatus
+    LastHeartbeatTime  util.Time
+    LastTransitionTime util.Time
+    Reason             string
+    Message            string
+}
+```
+
+## Events
+
+Job controller will be emitting the following events:
+* JobStart
+* JobFinish
+
+## Future evolution
+
+Below are the possible future extensions to the Job controller:
+* Be able to limit the execution time for a job, similarly to ActiveDeadlineSeconds for Pods.
+* Be able to create a chain of jobs dependent one on another.
+* Be able to specify the work each of the workers should execute (see type 1 from
+  [this comment](https://github.com/GoogleCloudPlatform/kubernetes/issues/1624#issuecomment-97622142))
+* Be able to inspect Pods running a Job, especially after a Job has finished, e.g.
+  by providing pointers to Pods in the JobStatus ([see comment](https://github.com/kubernetes/kubernetes/pull/11746/files#r37142628)).
+
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