Managing deployment processes

You can start a rollout to begin the deployment process of your application.

Procedure

To start a new deployment process from an existing DeploymentConfig object, run the following command:

Viewing a deployment

You can view a deployment to get basic information about all the available revisions of your application.

Procedure

To show details about all recently created replication controllers for the provided DeploymentConfig object, including any currently running deployment process, run the following command:
```
$ oc rollout history dc/<name>
```
To view details specific to a revision, add the --revision flag:
```
$ oc rollout history dc/<name> --revision=1
```
For more detailed information about a DeploymentConfig object and its latest revision, use the oc describe command:
```
$ oc describe dc <name>
```

Retrying a deployment

If the current revision of your DeploymentConfig object failed to deploy, you can restart the deployment process.

Procedure

To restart a failed deployment process:
```
$ oc rollout retry dc/<name>
```
If the latest revision of it was deployed successfully, the command displays a message and the deployment process is not retried.

Retrying a deployment restarts the deployment process and does not create a new deployment revision. The restarted replication controller has the same configuration it had when it failed.

Rolling back a deployment

Rollbacks revert an application back to a previous revision and can be performed using the REST API, the CLI, or the web console.

Procedure

To rollback to the last successful deployed revision of your configuration:
```
$ oc rollout undo dc/<name>
```
The DeploymentConfig object’s template is reverted to match the deployment revision specified in the undo command, and a new replication controller is started. If no revision is specified with --to-revision, then the last successfully deployed revision is used.
Image change triggers on the DeploymentConfig object are disabled as part of the rollback to prevent accidentally starting a new deployment process soon after the rollback is complete.

To re-enable the image change triggers:

Deployment configs also support automatically rolling back to the last successful revision of the configuration in case the latest deployment process fails. In that case, the latest template that failed to deploy stays intact by the system and it is up to users to fix their configurations.

You can add a command to a container, which modifies the container’s start-up behavior by overruling the image’s ENTRYPOINT. This is different from a lifecycle hook, which instead can be run once per deployment at a specified time.

Procedure

  containers:
  - name: <container_name>
    image: 'image'
    command:
      - '<command>'
    args:
      - '<argument_1>'
      - '<argument_2>'
      - '<argument_3>'

For example, to execute the java command with the -jar and /opt/app-root/springboots2idemo.jar arguments:

spec:
  containers:
  - name: example-spring-boot
    image: 'image'
    command:
      - java
    args:
      - /opt/app-root/springboots2idemo.jar

Viewing deployment logs

Procedure

To stream the logs of the latest revision for a given DeploymentConfig object:
```
$ oc logs -f dc/<name>
```
If the latest revision is running or failed, the command returns the logs of the process that is responsible for deploying your pods. If it is successful, it returns the logs from a pod of your application.
You can also view logs from older failed deployment processes, if and only if these processes (old replication controllers and their deployer pods) exist and have not been pruned or deleted manually:
```
$ oc logs --version=1 dc/<name>
```

Deployment triggers

A DeploymentConfig object can contain triggers, which drive the creation of new deployment processes in response to events inside the cluster.

If no triggers are defined on a DeploymentConfig object, a config change trigger is added by default. If triggers are defined as an empty field, deployments must be started manually.

Config change deployment triggers

The config change trigger results in a new replication controller whenever configuration changes are detected in the pod template of the DeploymentConfig object.

Config change deployment trigger

triggers:
  - type: "ConfigChange"

Image change deployment triggers

The image change trigger results in a new replication controller whenever the content of an image stream tag changes (when a new version of the image is pushed).

Image change deployment trigger

1	If the `imageChangeParams.automatic` field is set to `false`, the trigger is disabled.

With the above example, when the latest tag value of the origin-ruby-sample image stream changes and the new image value differs from the current image specified in the DeploymentConfig object’s helloworld container, a new replication controller is created using the new image for the helloworld container.

If an image change trigger is defined on a DeploymentConfig object (with a config change trigger and automatic=false, or with automatic=true) and the image stream tag pointed by the image change trigger does not exist yet, the initial deployment process will automatically start as soon as an image is imported or pushed by a build to the image stream tag.

Setting deployment triggers

Procedure

You can set deployment triggers for a DeploymentConfig object using the oc set triggers command. For example, to set a image change trigger, use the following command:
```
$ oc set triggers dc/<dc_name> \
    --from-image=<project>/<image>:<tag> -c <container_name>
```

Setting deployment resources

A deployment is completed by a pod that consumes resources (memory, CPU, and ephemeral storage) on a node. By default, pods consume unbounded node resources. However, if a project specifies default container limits, then pods consume resources up to those limits.

The minimum memory limit for a deployment is 12 MB. If a container fails to start due to a Cannot allocate memory pod event, the memory limit is too low. Either increase or remove the memory limit. Removing the limit allows pods to consume unbounded node resources.

You can also limit resource use by specifying resource limits as part of the deployment strategy. Deployment resources can be used with the recreate, rolling, or custom deployment strategies.

Procedure

In the following example, each of resources, cpu, memory, and ephemeral-storage is optional:
```
type: "Recreate"
  limits:
    cpu: "100m" (1)
    memory: "256Mi" (2)
    ephemeral-storage: "1Gi" (3)
```
However, if a quota has been defined for your project, one of the following two items is required:
- A resources section set with an explicit :
```
  type: "Recreate"
  resources:
    requests: (1)
      cpu: "100m"
      memory: "256Mi"
      ephemeral-storage: "1Gi"
```
  1 The requests object contains the list of resources that correspond to the list of resources in the quota.
To set deployment resources, choose one of the above options. Otherwise, deploy pod creation fails, citing a failure to satisfy quota.

In addition to rollbacks, you can exercise fine-grained control over the number of replicas by manually scaling them.

Pods can also be auto-scaled using the oc autoscale command.

Procedure

To manually scale a DeploymentConfig object, use the oc scale command. For example, the following command sets the replicas in the frontend DeploymentConfig object to 3.
```
$ oc scale dc frontend --replicas=3
```
The number of replicas eventually propagates to the desired and current state of the deployment configured by the DeploymentConfig object frontend.

Accessing private repositories from DeploymentConfig objects

You can add a secret to your DeploymentConfig object so that it can access images from a private repository. This procedure shows the OKD web console method.

Procedure

Create a new project.
From the Workloads page, create a secret that contains credentials for accessing a private image repository.
Create a DeploymentConfig object.
On the DeploymentConfig object editor page, set the Pull Secret and save your changes.

Assigning pods to specific nodes

You can use node selectors in conjunction with labeled nodes to control pod placement.

Cluster administrators can set the default node selector for a project in order to restrict pod placement to specific nodes. As a developer, you can set a node selector on a Pod configuration to restrict nodes even further.

Procedure

To add a node selector when creating a pod, edit the Pod configuration, and add the nodeSelector value. This can be added to a single Pod configuration, or in a Pod template:

apiVersion: v1
kind: Pod
spec:
  nodeSelector:
    disktype: ssd
...

Pods created when the node selector is in place are assigned to nodes with the specified labels. The labels specified here are used in conjunction with the labels added by a cluster administrator.

For example, if a project has the type=user-node and region=east labels added to a project by the cluster administrator, and you add the above disktype: ssd label to a pod, the pod is only ever scheduled on nodes that have all three labels.

Labels can only be set to one value, so setting a node selector of region=west in a Pod configuration that has region=east as the administrator-set default, results in a pod that will never be scheduled.

Running a pod with a different service account

You can run a pod with a service account other than the default.

Procedure

Edit the DeploymentConfig object:
Add the serviceAccount and serviceAccountName parameters to the spec field, and specify the service account you want to use:
```
spec:
  securityContext: {}
  serviceAccountName: <service_account>
```