Environment variables

Environment variables allows you to inject configuration into the applications running in the edge

Environment variables are a standard way to configure your applications. Typically, you can set them directly on the application:

name: example-app
scheduling:
  type: AllDevices
spec:
  containers:
  - name: my-app
    image: docker.io/my-org/my-app:latest
    env:
    - name: ADMIN_PASSWORD
      fromSecret: credentials # Value taken from secret named 'credentials'
    - name: ADMIN_USERNAME
      value: administrator # Value taken directly

Inheriting From Device

Synpse provides a mechanism to inject device environment variables to your applications.

You can either manually specify custom environment variables for each device or you can also specify them on the registration token during the provisioning.

Setting environment variables on a device (web user)

To set an environment variable for a device:

1. Open the device details

2. Click on the "New env var" button

3. Enter environment variable name and value

Adding environment variable to the device

Now, any application that is deployed on that device, will get the environment variable:

TZ=Europe/London

You can have multiple environment variables on each device.

You can use device environment variables to specify some customer related data so your applications can display tailored information based on where they get deployed.

Synpse Provided Environment Variables

Synpse provides certain metadata for the applications as environment variables. It's up to the application to use these environment variables or ignore them.

Environment Variable	Description	Example Value
SYNPSE_DEVICE_NAME	Device name in Synpse	powerplant-42
SYNPSE_DEVICE_IP	Device IP address	192.168.1.111
SYNPSE_DEVICE_HOSTNAME	Device hostname	rasp4-node
SYNPSE_DEVICE_ARCH	CPU architecture	arm
SYNPSE_PROJECT_ID	Project ID	prj_1r1pqWAG...
SYNPSE_NAMESPACE_ID	Namespace ID	nms_1r1pqW4d...
SYNPSE_APPLICATION_ID	Application ID	app_1a812qwe...

These environment variables are always available for applications running under Synpse. No additional settings are required.

Substitution

Synpse provides the ability to expand, or substitute, application and device metadata to facilitate dynamic application configurations.

Example Device Substitution

Let's say you have set an environment variable on the device called:

REGION=sillicon-valley

Now, you can use that environment variable to create something else, for example a URL on which the device will be accessible by users (assuming you have configured domain, etc.):

name: example-app
scheduling:
  type: AllDevices
spec:
  containers:
  - name: my-app
    image: docker.io/my-org/my-app:latest
    env:
    - name: PUBLIC_ADDRESS
      value: https://${REGION}.example.com

And your application will then see an environment variable which equals

PUBLIC_ADDRESS=https://sillicon-valley.example.com

String Operations

Synpse provides partial emulation for bash string operations. This can be used to manipulate string values prior to substitution.

• Example variable substitution with substring:

name: example-app
scheduling:
  type: AllDevices
spec:
  containers:
  - name: my-app
    image: docker.io/my-org/my-app:latest
    env:
    - name: CUSTOMER
      value: ${CUSTOMER_ID:0:4} # Getting first 4 symbols

Synpse emulates the below string operations:

${parameter^}
${parameter^^}
${parameter,}
${parameter,,}
${parameter:position}
${parameter:position:length}
${parameter#substring}
${parameter##substring}
${parameter%substring}
${parameter%%substring}
${parameter/substring/replacement}
${parameter//substring/replacement}
${parameter/#substring/replacement}
${parameter/%substring/replacement}
${#parameter}
${parameter=default}
${parameter:=default}
${parameter:-default}

Synpse makes a best-effort to emulate these operations however we do not promise perfect emulation.

Escaping

If you do not want the system to evaluate an expression it must be escaped:

name: example-app
scheduling:
  type: AllDevices
spec:
  containers:
  - name: my-app
    image: docker.io/my-org/my-app:latest
    env:
    - name: DEVICE_NAME
      value: $${MY_DEVICE_NAME}