Using container image staging
Container image staging on the SC//Reliantâ„¢ platform pre-pulls container images to your edge nodes in the background, ahead of the deployments that use them. New versions then roll out faster because the image is already on the node by the time Puppet activates it. Image Staging is especially valuable on slower network links, where pulling a fresh image at deployment time would extend the deployment window.
This page describes the Image Staging parameters and the procedures for enabling and disabling staging on a node group.
Considerations
- Image Staging is highly recommended for nodes on slower network links, since it ensures images are pulled in advance rather than at deployment time.
- Disabling Image Staging means container images will no longer be pre-pulled. Images will be fetched on-demand at deployment time, which may increase deployment duration on slower networks.
Parameters
| Property | Description | Example |
|---|---|---|
| Cron Entry | Defines how frequently the staging job runs, expressed as a standard cron expression. | 0 0 * * * (runs every day at midnight) |
| Images | Specifies which Docker images to include in the staging schedule. If left empty, all container images are included. | One image per line in image:tag format. The tag is optional. |
| Jitter | A random delay (in seconds) introduced before each image pull begins. This prevents multiple nodes from hitting the registry simultaneously (cron collision avoidance). | 5 seconds |
| Stagger | A fixed delay (in seconds) inserted between each sequential image pull. This reduces load on the image registry and network. | 10 seconds |
For a quick reference of common cron expressions, see the cron expression reference on the Image Management overview.
Enabling Image Staging
- Navigate to the node group Hash configuration page.
- Locate the Image Staging section.
- Click the Enable this option toggle in the top-right corner of the Image Staging panel so that it turns blue/on.
- In the Cron Entry text field, enter a valid cron expression for the staging schedule. For example,
0 0 * * *stages images every day at midnight. - (Optional) In the Images textarea, enter specific Docker images to stage, one per line in
image:tagformat. Leave blank to stage all container images. - (Optional) Set a Jitter value (in seconds) to randomize pull start times and avoid registry collisions. The default is
5. - (Optional) Set a Stagger value (in seconds) to introduce a delay between sequential image pulls. The default is
10. - Save the configuration using the page's save/apply action.
đŸ’¡ Tip: Image Staging is highly recommended for nodes on slower network links, since it ensures images are pulled in advance rather than at deployment time.
Disabling Image Staging
- Navigate to the node group Hash configuration page.
- Locate the Image Staging section.
- Click the Enable this option toggle in the top-right corner of the Image Staging panel so that it turns gray/off.
- Save the configuration using the page's save/apply action.
Note: Disabling Image Staging means container images will no longer be pre-pulled. Images will be fetched on-demand at deployment time, which may increase deployment duration on slower networks.