The host requirements section of the yaml gives Replicated the ability to analyze system requirements and warn or prevent the user from proceeding with an installation or upgrade. In addition to host requirements, Replicated has the ability to define fully customizable preflight requirements as of version v2.30.0 . These programmable requirements provide flexibility to the point that an arbitrary command can be executed by a vendor provided image. See the commands section below for a full list of commands that may be run including examples.
Commands
Commands will be run to determine the status of a requirement. They return result messages, a status code and an error. Next we will look at examples. For details on the fields please see the resource specification section at the bottom of the page.
Scheduler
Run a preflight check using your own Service definition.
To begin using custom raw preflight commands, add a Service spec to your release yaml with kind preflight-swarm, then configure a scheduler command to use it in the custom_requirements section of your Replicated yaml.
Example
---
# kind: replicated
custom_requirements:
- id: license-file-exists
message: License file exists
details: The vendor license file must exist on the host at /etc/vendor-license
results:
- status: success
message: File /etc/vendor-license exists.
condition:
status_code: 0
- status: error
message: File /etc/vendor-license does not exists.
condition:
status_code: 1
command:
id: scheduler
timeout: 15
data:
swarm:
service: "license-checker" # matches the Service name below
---
# kind: preflight-swarm
version: "3"
services:
license-checker:
image: busybox:latest
volumes:
- "/etc:/host/etc"
command: ["test", "-e", "/host/etc/vendor-license"]Example: Running checks on specific nodes
In certain cases, you may want to limit which nodes certain requirements apply to. You can use placement to
limit checks to only run on specific nodes. For example, you may only want to run performance checks on GPU-equipped nodes, but not on general web-app nodes.
---
# kind: replicated
custom_requirements:
- id: gpu-node-has-gpu-access
message: Nodes labeled with role=gpu have GPUs
details: Nodes labeled with role=gpu must have access to GPU functionality
results:
- status: success
message: GPU performance check succeeded
condition:
status_code: 0
- status: error
message: Unable to check for GPU on node
condition:
status_code: 1
command:
id: scheduler
timeout: 120
data:
swarm:
service: "gpu-checker" # matches the Service name below
placement:
constraints:
- node.labels.role==gpu
---
# kind: preflight-swarm
version: "3"
services:
gpu-checker:
image: registry.replicated.com/myapp/gpu_perf_checker:1.0.0
command: ["/scripts/ensure_gpu.sh"]TCP Dial
Example
custom_requirements:
- id: tcp-dial-github
message: Can access github.com
details: Can connect to the address github.com:443.
results:
- status: success
message: Successful connection to the address github.com:443.
condition:
status_code: 0
- status: error
message: Failed to connect to the address github.com:443.
condition:
status_code: 111
- status: warn
message:
default_message: 'Invalid status code {{.status}}. ERROR: {{.error}}'
args:
status: '{{repl .StatusCode }}'
error: '{{repl .Error }}'
# else error
command:
id: tcp_dial
data:
addr: 'github.com:443'
cluster: falseHTTP Request
Example
custom_requirements:
- id: http-request-github
message: Can access github.com
details: Can connect to address https://github.com.
results:
- status: success
message: Successful connection to the address github.com.
condition:
status_code: 200
- status: error
message:
default_message: 'Invalid status code {{.status}}. ERROR: {{.error}}'
args:
status: '{{repl .StatusCode }}'
error: '{{repl .Error }}'
# else error
command:
id: http_request
data:
url: 'https://github.com'
method: 'HEAD'
cluster: falseResource Specification
Custom requirements are represented with the followings and properties.
Requirement
The requirement resource is the primary resource for Programmable Preflight Checks. A requirement represents a single check that is to be preformed during the installation and upgrade steps of the application lifecycle.
| Name | Type | Required | Description |
|---|---|---|---|
| id | string | yes | A unique identifier for the requirement |
| message | string or Message | yes | A short description of the requirement |
| details | string or Message | no | A more detailed description of the requirement |
| when | string | no | Will determine if this requirement should be run (evaluated to a boolean value) |
| command | Command | yes | The command that will be run |
| results | array[Result] | yes | An array of result objects that when evaluated will determine success or failure |