Using Services in Apps
This topic provides usage guidance for binding all a9s Data Services to Cloud Foundry apps.
Binding Information
Binding information is delivered to apps via the VCAP_SERVICES
environment
variable. This variable is a JSON object string.
Structure
- hash of services (e.g a9s-redis7, a9s-postgresql11...)
- array of service instances
name
string
tags
array
of tag asstrings
credentials
- service specific credentials
- array of service instances
Environment Variable Example
VCAP_SERVICES
:
{
"a9s-rabbitmq310": [
{
"name": "example-rabbitdb",
"tags": [ "rabbitmq" ],
"credentials": {
"host": "localhost",
"password": "quest",
"port": 5672,
"uri": "amqp://guest:guest@localhost:5672",
"username": "guest"
}
}
]
}
Best Practices
- Do not rely on order in
VCAP_SERVICES
- Do not rely on service versions
- Do not hard code service instance names
Suggested Practices
Option A
Specify the service name via an environment viable with your app manifest. This is trivial to implement in an app, and follows the best practices making it easy to rebind an apps without changing code in your app.
Option B
Look for a service instance with a tag, that can be hard coded in an app, without compromising the best practices. This is trivial to implement, but you must clearly document the tag you have hard coded. The advantage of this option is not having to update a variable in an app manifest when rebinding.
RabbitMQ Go Example
Here you can find a RabbitMQ example of how to simultaneously implement suggested practices A and B in an app.