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Chapter 10. Running Jobs on Hosts


You can run jobs on hosts remotely from Capsules using shell scripts or Ansible tasks and playbooks. This is referred to as remote execution.

For custom Ansible roles that you create, or roles that you download, you must install the package containing the roles on the Capsule base operating system. Before you can use Ansible roles, you must import the roles into Satellite from the Capsule where they are installed.

Communication occurs through Capsule Server, which means that Satellite Server does not require direct access to the target host, and can scale to manage many hosts. Remote execution uses the SSH service that must be enabled and running on the target host. Ensure that the remote execution Capsule has access to port 22 on the target hosts.

Satellite uses ERB syntax job templates. For more information, see Appendix A, Template Writing Reference.

Several job templates for shell scripts and Ansible are included by default. For more information, see Section 10.6.1, “Setting up Job Templates”.

By default, Satellite Server is configured to use the Katello Agent rather than remote execution. To change this setting, navigate to Administer > Settings, click Content, and change the Use remote execution by default setting.

Note

Any Capsule Server base operating system is a client of Satellite Server’s internal Capsule, and therefore this section applies to any type of host connected to Satellite Server, including Capsule Servers.

You can run jobs on multiple hosts at once, and you can use variables in your commands for more granular control over the jobs you run. You can use host facts, smart class parameters, smart variables, and host parameters to populate variable values. For more information about Ansible variables, see Overriding Ansible Variables in Satellite. In addition, you can specify custom values for templates when you run the command. For more information, see Section 10.6.2, “Executing Jobs”.

10.1. How Satellite Selects Capsule for Remote Execution

When you run a remote job on hosts, for every host, Satellite performs the following actions to find a remote execution Capsule to use. Satellite searches only for Capsules that have the remote execution feature enabled.

  1. Satellite finds the host’s interfaces that have the Remote execution check box selected.
  2. Satellite finds the subnets of these interfaces.
  3. Satellite finds remote execution Capsules assigned to these subnets.
  4. From this set of Capsules, Satellite selects the Capsule that has the least number of running jobs. By doing this, Satellite ensures that the jobs load is balanced between remote execution Capsules.
  5. If Satellite does not find a remote execution Capsule at this stage, and if the Fallback to Any Capsule setting is enabled, Satellite adds another set of Capsules to select the remote execution Capsule from. Satellite selects the most lightly loaded Capsule from the following types of Capsules that are assigned to the host:

    • DHCP, DNS and TFTP Capsules assigned to the host’s subnets
    • DNS Capsule assigned to the host’s domain
    • Realm Capsule assigned to the host’s realm
    • Puppet Master Capsule
    • Puppet CA Capsule
    • OpenSCAP Capsule
  6. If Satellite does not find a remote execution Capsule at this stage, and if the Enable Global Capsule setting is enabled, Satellite selects the most lightly loaded remote execution Capsule from the set of all Capsules in the host’s organization and location to execute a remote job.

10.1.1. Configuring the Fallback to Any Capsule Remote Execution Setting in Satellite

You can enable the Fallback to Any Capsule setting to configure Satellite to search for remote execution Capsules from the list of Capsules that are assigned to hosts. This can be useful if you need to run remote jobs on hosts that have no subnets configured or if the hosts' subnets are assigned to Capsules that do not have the remote execution feature enabled.

If the Fallback to Any Capsule setting is enabled, Satellite adds another set of Capsules to select the remote execution Capsule from. Satellite also selects the most lightly loaded Capsule from the set of all Capsules assigned to the host, such as the following:

  • DHCP, DNS and TFTP Capsules assigned to the host’s subnets
  • DNS Capsule assigned to the host’s domain
  • Realm Capsule assigned to the host’s realm
  • Puppet Master Capsule
  • Puppet CA Capsule
  • OpenSCAP Capsule

Procedure

  1. In the Satellite web UI, navigate to Administer > Settings.
  2. Click RemoteExecution.
  3. Configure the Fallback to Any Capsule setting.

For CLI Users

Enter the hammer settings set command on Satellite to configure the Fallback to Any Capsule setting. For example, to set the value to true, enter the following command:

# hammer settings set --name=remote_execution_fallback_proxy --value=true

10.1.2. Configuring the Global Capsule Remote Execution Setting in Satellite

By default, Satellite searches for remote execution Capsules in hosts' organizations and locations regardless of whether Capsules are assigned to hosts' subnets or not. You can disable the Enable Global Capsule setting if you want to limit the search to the Capsules that are assigned to hosts' subnets.

If the Enable Global Capsule setting is enabled, Satellite adds another set of Capsules to select the remote execution Capsule from. Satellite also selects the most lightly loaded remote execution Capsule from the set of all Capsules in the host’s organization and location to execute a remote job.

Procedure

  1. In the Satellite web UI, navigate to Administer > Settings.
  2. Click RemoteExection.
  3. Configure the Enable Global Capsule setting.

For CLI Users

Enter the hammer settings set command on Satellite to configure the Enable Global Capsule setting. For example, to set the value to true, enter the following command:

# hammer settings set --name=remote_execution_global_proxy --value=true

10.2. Configuring Satellite to Use an Alternative Directory to Execute Remote Jobs on Clients

By default, Satellite uses the /var/tmp directory on the client system to execute the remote execution jobs. If the client system has noexec set for the /var/ volume or file system, you must configure Satellite to use an alternative directory because otherwise the remote execution job fails since the script cannot be run.

Procedure

Optional: To use an alternative directory, complete this procedure.

  1. Create a new directory, for example new_place:

    # mkdir /remote_working_dir
  2. Copy the SELinux context from the default var directory:

    # chcon --reference=/var /remote_working_dir
  3. Edit the remote_working_dir setting in the /etc/foreman-proxy/settings.d/remote_execution_ssh.yml file to point to the required directory, for example:

    :remote_working_dir: /remote_working_dir

10.3. Distributing SSH Keys for Remote Execution

To use SSH keys for authenticating remote execution connections, you must distribute the public SSH key from Capsule to its attached hosts that you want to manage. Ensure that the SSH service is enabled and running on the hosts. Configure any network or host-based firewalls to enable access to port 22.

Use one of the following methods to distribute the public SSH key from Capsule to target hosts:

Satellite distributes SSH keys for the remote execution feature to the hosts provisioned from Satellite by default.

If the hosts are running on Amazon Web Services, enable password authentication. For more information, see https://aws.amazon.com/premiumsupport/knowledge-center/ec2-password-login/.

10.3.1. Distributing SSH Keys for Remote Execution Manually

To distribute SSH keys manually, complete the following steps:

Procedure

  1. Enter the following command on Capsule. Repeat for each target host you want to manage:

    # ssh-copy-id -i ~foreman-proxy/.ssh/id_rsa_foreman_proxy.pub root@target.example.com
  2. To confirm that the key was successfully copied to the target host, enter the following command on Capsule:

    # ssh -i ~foreman-proxy/.ssh/id_rsa_foreman_proxy root@target.example.com

10.3.2. Using the Satellite API to Obtain SSH Keys for Remote Execution

To use the Satellite API to download the public key from Capsule, complete this procedure on each target host.

Procedure

  1. On the target host, create the /.ssh directory to store the SSH key:

    # mkdir ~/.ssh
  2. Download the SSH key from Capsule:

    # curl https://capsule.example.com:9090/ssh/pubkey >> ~/.ssh/authorized_keys
  3. Configure permissions for the ~/.ssh directory:

    # chmod 700 ~/.ssh
  4. Configure permissions for the authorized_keys file:

    # chmod 600 ~/.ssh/authorized_keys

10.3.3. Configuring a Kickstart Template to Distribute SSH Keys during Provisioning

You can add a remote_execution_ssh_keys snippet to your custom kickstart template to deploy SSH Keys to hosts during provisioning. Kickstart templates that Satellite ships include this snippet by default. Therefore, Satellite copies the SSH key for remote execution to the systems during provisioning.

Procedure

  • To include the public key in newly-provisioned hosts, add the following snippet to the Kickstart template that you use:

    <%= snippet 'remote_execution_ssh_keys' %>

10.4. Configuring a keytab for Kerberos Ticket Granting Tickets

Use this procedure to configure Satellite to use a keytab to obtain Kerberos ticket granting tickets. If you do not set up a keytab, you must manually retrieve tickets.

Procedure

To ensure that the foreman-proxy user on Satellite can obtain Kerberos ticket granting tickets, complete the following steps:

  1. Find the ID of the foreman-proxy user:

    # id -u foreman-proxy
  2. Modify the umask value so that new files have the permissions 600:

    # umask 077
  3. Create the directory for the keytab:

    # mkdir -p "/var/kerberos/krb5/user/USER_ID"
  4. Create a keytab or copy an existing keytab to the directory:

    # cp your_client.keytab /var/kerberos/krb5/user/USER_ID/client.keytab
  5. Change the directory owner to the foreman-proxy user:

    # chown -R foreman-proxy:foreman-proxy "/var/kerberos/krb5/user/USER_ID"
  6. Ensure that the keytab file is read-only:

    # chmod -wx "/var/kerberos/krb5/user/USER_ID/client.keytab"
  7. Restore the SELinux context:

    # restorecon -RvF /var/kerberos/krb5

10.5. Configuring Kerberos Authentication for Remote Execution

From Satellite 6.7, you can use Kerberos authentication to establish an SSH connection for remote execution on Satellite hosts.

Prerequisites

Before you can use Kerberos authentication for remote execution on Red Hat Satellite, you must set up a Kerberos server for identity management and ensure that you complete the following prerequisites:

  • Enroll Satellite Server on the Kerberos server
  • Enroll the Satellite target host on the Kerberos server
  • Configure and initialize a Kerberos user account for remote execution
  • Ensure that the foreman-proxy user on Satellite has a valid Kerberos ticket granting ticket

Procedure

To set up Satellite to use Kerberos authentication for remote execution on hosts, complete the following steps:

  1. To install the tfm-rubygem-net-ssh-krb package, enter the following command:

    # yum install tfm-rubygem-net-ssh-krb
  2. To install and enable Kerberos authentication for remote execution, enter the following command:

    # satellite-installer --scenario satellite \
     --foreman-proxy-plugin-remote-execution-ssh-ssh-kerberos-auth true
  3. To edit the default user for remote execution, in the Satellite web UI, navigate to Administer > Settings and click the RemoteExecution tab. In the SSH User row, edit the second column and add the user name for the Kerberos account.
  4. Navigate to remote_execution_effective_user and edit the second column to add the user name for the Kerberos account.

To confirm that Kerberos authentication is ready to use, run a remote job on the host.

10.6. Configuring and Running Remote Jobs

Any command that you want to apply to a remote host must be defined as a job template. After you have defined a job template you can execute it multiple times.

10.6.1. Setting up Job Templates

Satellite provides default job templates that you can use for executing jobs. To view the list of job templates, navigate to Hosts > Job templates. If want to use a template without making changes, proceed to Section 10.6.2, “Executing Jobs”.

You can use default templates as a base for developing your own. Default job templates are locked for editing. Clone the template and edit the clone.

  1. To clone a template, in the Actions column, select Clone.
  2. Enter a unique name for the clone and click Submit to save the changes.

Job templates use the Embedded Ruby (ERB) syntax. For more information about writing templates, see the Appendix A, Template Writing Reference.

Ansible Considerations

To create an Ansible job template, use the following procedure and instead of ERB syntax, use YAML syntax. Begin the template with --- and to the first line, you must add - hosts: all. You can embed an Ansible playbook YAML file into the job template body. You can also add ERB syntax to customize your YAML Ansible template. You can also import Ansible playbooks in Satellite. For more information, see Chapter 13, Synchronizing Template Repositories.

Parameter Variables

At run time, job templates can accept parameter variables that you define for a host. Note that only the parameters visible on the Parameters tab at the host’s edit page can be used as input parameters for job templates. If you do not want your Ansible job template to accept parameter variables at run time, in the Satellite web UI, navigate to Administer > Settings and click the Ansible tab. In the Top level Ansible variables row, change the Value parameter to No.

To Create a Job Template:

  1. Navigate to Hosts > Job templates.
  2. Click New Job Template.
  3. Click the Template tab, and in the Name field, enter a unique name for your job template.
  4. Select Default to make the template available for all organizations and locations.
  5. Create the template directly in the template editor or upload it from a text file by clicking Import.
  6. Optional: In the Audit Comment field, add information about the change.
  7. Click the Job tab, and in the Job category field, enter your own category or select from the default categories listed in Table 10.1, “Default Job Template Categories”.
  8. Optional: In the Description Format field, enter a description template. For example, Install package %{package_name}. You can also use %{template_name} and %{job_category} in your template.
  9. From the Provider Type list, select SSH for shell scripts and Ansible for Ansible tasks or playbooks.
  10. Optional: In the Timeout to kill field, enter a timeout value to terminate the job if it does not complete.
  11. Optional: Click Add Input to define an input parameter. Parameters are requested when executing the job and do not have to be defined in the template. For examples, see the Help tab.
  12. Optional: Click Foreign input set to include other templates in this job.
  13. Optional: In the Effective user area, configure a user if the command cannot use the default remote_execution_effective_user setting.
  14. Optional: If this template is a snippet to be included in other templates, click the Type tab and select Snippet.
  15. Click the Location tab and add the locations where you want to use the template.
  16. Click the Organizations tab and add the organizations where you want to use the template.
  17. Click Submit to save your changes.

You can create advanced templates by including other templates in the template syntax, see Section 10.6.4, “Creating Advanced Templates” for more information.

An advanced template is required, for example, for executing jobs that perform power actions; see Example 10.4, “Including Power Actions in Templates” for information on how to include the Power Action - SSH Default template in a custom template.

For CLI Users

To create a job template using a template-definition file, enter the following command:

# hammer job-template create \
--file "path_to_template_file" \
--name "template_name" \
--provider-type SSH \
--job-category "category_name"
Table 10.1. Default Job Template Categories
Job template categoryDescription

Packages

Templates for performing package related actions. Install, update, and remove actions are included by default.

Puppet

Templates for executing Puppet runs on target hosts.

Power

Templates for performing power related actions. Restart and shutdown actions are included by default.

Commands

Templates for executing custom commands on remote hosts.

Services

Templates for performing service related actions. Start, stop, restart, and status actions are included by default.

Katello

Templates for performing content related actions. These templates are used mainly from different parts of the Satellite web UI (for example bulk actions UI for content hosts), but can be used separately to perform operations such as errata installation.

Example 10.1. Creating a restorecon Template

This example shows how to create a template called Run Command - restorecon that restores the default SELinux context for all files in the selected directory on target hosts.

  1. Navigate to Hosts > Job templates. Click New Job Template.
  2. Enter Run Command - restorecon in the Name field. Select Default to make the template available to all organizations. Add the following text to the template editor:

    restorecon -RvF <%= input("directory") %>

    The <%= input("directory") %> string is replaced by a user-defined directory during job invocation.

  3. On the Job tab, set Job category to Commands.
  4. Click Add Input to allow job customization. Enter directory to the Name field. The input name must match the value specified in the template editor.
  5. Click Required so that the command cannot be executed without the user specified parameter.
  6. Select User input from the Input type list. Enter a description to be shown during job invocation, for example Target directory for restorecon.
  7. Click Submit.

See Example 10.2, “Executing a restorecon Template on Multiple Hosts” for information on how to execute a job based on this template.

10.6.2. Executing Jobs

You can execute a job that is based on a job template against one or more hosts.

Procedure

  1. Navigate to Hosts > All Hosts and select the target hosts on which you want to execute a remote job. You can use the search field to filter the host list.
  2. From the Select Action list, select Schedule Remote Job.
  3. On the Job invocation page, define the main job settings:

    1. Select the Job category and the Job template you want to use.
    2. Optional: Select a stored search string in the Bookmark list to specify the target hosts.
    3. Optional: Further limit the targeted hosts by entering a Search query. The Resolves to line displays the number of hosts affected by your query. Use the refresh button to recalculate the number after changing the query. The preview icon lists the targeted hosts.
    4. The remaining settings depend on the selected job template. See To Create a Job Template: for information on adding custom parameters to a template.
  4. Optional: To configure advanced settings for the job, click Display advanced fields. Some of the advanced settings depend on the job template, the following settings are general:

    • Effective user defines the user for executing the job, by default it is the SSH user.
    • Concurrency level defines the maximum number of jobs executed at once, which can prevent overload of systems' resources in a case of executing the job on a large number of hosts.
    • Timeout to kill defines time interval in seconds after which the job should be killed, if it is not finished already. A task which could not be started during the defined interval, for example, if the previous task took too long to finish, is canceled.
    • Type of query defines when the search query is evaluated. This helps to keep the query up to date for scheduled tasks.
    • Execution ordering determines the order in which the job is executed on hosts: alphabetical or randomized.

      Concurrency level and Timeout to kill settings enable you to tailor job execution to fit your infrastructure hardware and needs.

  5. To run the job immediately, ensure that Schedule is set to Execute now. You can also define a one-time future job, or set up a recurring job. For recurring tasks, you can define start and end dates, number and frequency of runs. You can also use cron syntax to define repetition. For more information about cron, see the Automating System Tasks section of the Red Hat Enterprise Linux 7 System Administrator’s Guide.
  6. Click Submit. This displays the Job Overview page, and when the job completes, also displays the status of the job.

For CLI Users

Enter the following command on Satellite:

+

# hammer settings set --name=remote_execution_global_proxy --value=false

To execute a remote job with custom parameters, complete the following steps:

  1. Find the ID of the job template you want to use:

    # hammer job-template list
  2. Show the template details to see parameters required by your template:

    # hammer job-template info --id template_ID
  3. Execute a remote job with custom parameters:

    # hammer job-invocation create \
    --job-template "template_name" \
    --inputs key1="value",key2="value",... \
    --search-query "query"

    Replace query with the filter expression that defines hosts, for example "name ~ rex01". For more information about executing remote commands with hammer, enter hammer job-template --help and hammer job-invocation --help.

Example 10.2. Executing a restorecon Template on Multiple Hosts

This example shows how to run a job based on the template created in Example 10.1, “Creating a restorecon Template” on multiple hosts. The job restores the SELinux context in all files under the /home/ directory.

  1. Navigate to Hosts > All hosts and select target hosts. Select Schedule Remote Job from the Select Action list.
  2. In the Job invocation page, select the Commands job category and the Run Command - restorecon job template.
  3. Type /home in the directory field.
  4. Set Schedule to Execute now.
  5. Click Submit. You are taken to the Job invocation page where you can monitor the status of job execution.

10.6.3. Monitoring Jobs

You can monitor the progress of the job while it is running. This can help in any troubleshooting that may be required.

Ansible jobs run on batches of 100 hosts, so you cannot cancel a job running on a specific host. A job completes only after the Ansible playbook runs on all hosts in the batch.

To Monitor a Job:

  1. Navigate to the Job page. This page is automatically displayed if you triggered the job with the Execute now setting. To monitor scheduled jobs, navigate to Monitor > Jobs and select the job run you wish to inspect.
  2. On the Job page, click the Hosts tab. This displays the list of hosts on which the job is running.
  3. In the Host column, click the name of the host that you want to inspect. This displays the Detail of Commands page where you can monitor the job execution in real time.
  4. Click Back to Job at any time to return to the Job Details page.

For CLI Users

To monitor the progress of a job while it is running, complete the following steps:

  1. Find the ID of a job:

    # hammer job-invocation list
  2. Monitor the job output:

    # hammer job-invocation output \
    --id job_ID \
    --host host_name
  3. Optional: to cancel a job, enter the following command:

    # hammer job-invocation cancel \
    --id job_ID

10.6.4. Creating Advanced Templates

When creating a job template, you can include an existing template in the template editor field. This way you can combine templates, or create more specific templates from the general ones.

The following template combines default templates to install and start the httpd service on Red Hat Enterprise Linux systems:

<%= render_template 'Package Action - SSH Default', :action => 'install', :package => 'httpd' %>
<%= render_template 'Service Action - SSH Default', :action => 'start', :service_name => 'httpd' %>

The above template specifies parameter values for the rendered template directly. It is also possible to use the input() method to allow users to define input for the rendered template on job execution. For example, you can use the following syntax:

<%= render_template 'Package Action - SSH Default', :action => 'install', :package => input("package") %>

With the above template, you have to import the parameter definition from the rendered template. To do so, navigate to the Jobs tab, click Add Foreign Input Set, and select the rendered template from the Target template list. You can import all parameters or specify a comma separated list.

Example 10.3. Rendering a restorecon Template

This example shows how to create a template derived from the Run command - restorecon template created in Example 10.1, “Creating a restorecon Template”. This template does not require user input on job execution, it will restore the SELinux context in all files under the /home/ directory on target hosts.

Create a new template as described in Section 10.6.1, “Setting up Job Templates”, and specify the following string in the template editor:

<%= render_template("Run Command - restorecon", :directory => "/home") %>

Example 10.4. Including Power Actions in Templates

This example shows how to set up a job template for performing power actions, such as reboot. This procedure prevents Satellite from interpreting the disconnect exception upon reboot as an error, and consequently, remote execution of the job works correctly.

Create a new template as described in Section 10.6.1, “Setting up Job Templates”, and specify the following string in the template editor:

<%= render_template("Power Action - SSH Default", :action => "restart") %>

10.7. Delegating Permissions for Remote Execution

You can control which users can run which jobs within your infrastructure, including which hosts they can target. The remote execution feature provides two built-in roles:

  • Remote Execution Manager: This role allows access to all remote execution features and functionality.
  • Remote Execution User: This role only allows running jobs; it does not provide permission to modify job templates.

You can clone the Remote Execution User role and customize its filter for increased granularity. If you adjust the filter with the view_job_templates permission, the user can only see and trigger jobs based on matching job templates. You can use the view_hosts and view_smart_proxies permissions to limit which hosts or Capsules are visible to the role.

The execute_template_invocation permission is a special permission that is checked immediately before execution of a job begins. This permission defines which job template you can run on a particular host. This allows for even more granularity when specifying permissions. For more information on working with roles and permissions see Creating and Managing Roles in the Administering Red Hat Satellite.

The following example shows filters for the execute_template_invocation permission:

name = Reboot and host.name = staging.example.com
name = Reboot and host.name ~ *.staging.example.com
name = "Restart service" and host_group.name = webservers

The first line in the above example permits the user to apply the Reboot template to one selected host. The second line defines a pool of hosts with names ending with .staging.example.com. The third line binds the template with a host group.

Note

Permissions assigned to users can change over time. If a user has already scheduled some jobs to run in the future, and the permissions have changed, this can result in execution failure because the permissions are checked immediately before job execution.

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