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Chapter 1. Managing device fleets

The Red Hat Edge Manager simplifies the management of a large number of devices and workloads through device fleets. A fleet is a resource that defines a group of devices governed by a common device template and management policies.

When you make a change to the device template, all devices in the fleet receive the changes when the Red Hat Edge Manager agent detects the new target specification.

Device monitoring in a fleet is also simplified because you can check the status summary of the whole fleet.

Fleet-level management offers the following advantages:

  • Scales your operations because you perform operations only once for each fleet instead of once for each device.
  • Minimizes the risk of configuration mistakes and configuration drift.
  • Automatically applies the target configuration when you add devices to the fleet or replace devices in the fleet.

The fleet specification consists of the following features:

Label selector
Determines which devices are part of the fleet.
Device template
Defines the configuration that the Red Hat Edge Manager enforces on devices in the fleet.
Policies
Govern how devices are managed, for example, how changes to the device template are rolled out to the devices.

You can have both individually managed and fleet-managed devices at the same time. When a device is selected into a fleet, the Red Hat Edge Manager creates the device specification for the new device based on the device template. If you update the device template for a fleet or a new device joins the fleet, the Red Hat Edge Manager enforces the new specification in the fleet.

If a device is not selected into any fleets, the device is considered user-managed or unmanaged. For user-managed devices, you must update the device specification either manually or through an external automation.

Important: A device cannot be member of more than one fleet at the same time.

For more information, see Labels and label selectors.

1.1. Device selection into a fleet
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By default, devices are not assigned to a fleet. Instead, each fleet uses a selector that defines which labels a device must have to be added to the fleet.

To understand how to use labels in a fleet, see the following example:

The following list shows point-of-sales terminal devices and their labels:

Expand

Device

Labels

A 

type: pos-terminal
, 
region: east
, 
stage: production

B 

type: pos-terminal
, 
region: east
, 
stage: development

C 

type: pos-terminal
, 
region: west
, 
stage: production

D 

type: pos-terminal
, 
region: west
, 
stage: development

If all point-of-sales terminals uses the same configuration and are managed by the same operations team, you can define a single fleet called 

pos-terminals
with the 
type=pos-terminal
label selector. Then, the fleet contains devices A, B, C, and D.

However, you might want to create separate fleets for the different organizations for development or production. You can define a fleet for development with the 

type=pos-terminal, stage=development
label selector, which selects devices C and D. Then, you can define another fleet for production with the 
type=pos-terminal, stage=production
label selector. By using the correct label selectors, you can manage both fleets independently.

Important: You must define selectors in a way that two fleets do not select the same device. For example, if one fleet selects 

region=east
, and another fleet selects 
stage=production
, both fleets try to select device A. If two fleets try to select the same device, the Red Hat Edge Manager keeps the device in the currently assigned fleet, if any, and sets the 
OverlappingSelectors
condition on the affected fleets to 
true
.

1.2. Device templates
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A device template of a fleet contains a device specification that is applied to all devices in the fleet when the template is updated.

For example, you can specify in the device template of a fleet that all devices in the fleet must run the 

quay.io/flightctl/rhel:9.5
operating system image.

The Red Hat Edge Manager service then rolls out the target specification to all devices in the fleet and the Red Hat Edge Manager agents update each devices accordingly.

You can change other specification items in the device template and the Red Hat Edge Manager apply the changes in the same way.

However, sometimes not all of the devices in the fleet need to have the exact same specification. The Red Hat Edge Manager allows templates to contain placeholders that are populated based on the device name or label values.

The syntax of the placeholders matches that of Go templates. However, you can only use simple text and actions.

The use of conditionals or loops in the placeholders is not supported.

You can reference anything from the metadata of a device, such as 

{{ .metadata.labels.key }}
or 
{{ .metadata.name }}
.

You can also use the following functions in your placeholders:

  • The 
    upper
    function changes the value to uppercase. For example, the function is 
    {{ upper .metadata.name }}
    .
  • The 
    lower
    function changes the value to lowercase. For example, the function is 
    {{ lower .metadata.labels.key }}
    .
  • The 
    replace
    function replaces all occurrences of a substring with another string. For example, the function is 
    {{ replace "old" "new" .metadata.labels.key }}
    .
  • The 
    getOrDefault
    function returns a default value if accessing a missing label. For example, he function is 
    {{ getOrDefault .metadata.labels "key" "default" }}
    .

You can combine the functions in pipelines, for example, a combined function is 

{{ getOrDefault .metadata.labels "key" "default" | upper | replace " " "-" }}
.

Note: Ensure using proper Go template syntax. For example, 

{{ .metadata.labels.target-revision }}
is not valid because of the hyphen. Instead, you must refer to the field as 
{{ index .metadata.labels "target-revision" }}
.

You can use the placeholders in device templates in the following ways:

  • You can label devices by deployment stage, for example, stage labels are 
    stage: testing
    and 
    stage: production
    . Then, you can use the label with the 
    stage
    key as placeholder when referencing the operating system image to use, for example, use 
    quay.io/myorg/myimage:latest-{{ .metadata.labels.stage }}
    or when referencing a configuration folder in a Git repository.
  • You can label devices by deployment site, for example, deployment sites are 
    site: factory-berlin
    and 
    site: factory-madrid
    .
  • Then, you can use the label with the 
    site
    key as parameter when referencing the secret with network access credentials in Kubernetes.

The following fields in device templates support placeholders:

Expand

Field

Placeholders supported in

Operating System Image

repository name, image name, image tag

Git Config Provider

target revision, path

HTTP Config Provider

URL suffix, path

Inline Config Provider

content, path

Define label selector to add devices into a fleet.

Complete the following tasks:

  1. Run the following command to verify that the label selector returns the devices that you want to add to the fleet: 

    flightctl get devices -l type=pos-terminal -l stage=development

  2. If running the command returns the expected list of devices, you can define a fleet that selects the devices by using the following YAML file: 

    apiVersion: flightctl.io/v1alpha1
kind: Fleet
metadata:
  name: my_fleet
spec:
  selector:
    matchLabels:
      type: pos-terminal
      stage: development
[...]

  3. Apply the change by running the following command: 

    flightctl apply -f my_fleet.yaml

  4. Check for any overlaps with the selector of other fleets by running the following command: 

    flightctl get fleets/my_fleet -o json | jq -r '.status.conditions[] | select(.type=="OverlappingSelectors").status'

    See the following example output: 

    False
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