How to change credentials for a given service in Cloud Foundry - mlab

Question

I would like to know how (and if it's possible) to change the URI credentials from a service in Cloud Foundry. More specifically, mLab service (free plan) from Pivotal Cloud Foundry.
Background
I created and pushed a nodejs app to Pivotal Cloud Foundry.
This app is bound to a mLab service using free plan.
When the mLab service was created using Pivotal website, it created a database with an user and password automatically.
Opening app settings inside Pivotal website, I can see the following environment variables. Please notice the mongo uri inside credentials and name inside mLab.
{
"staging_env_json": {},
"running_env_json": {},
"system_env_json": {
"VCAP_SERVICES": {
"mlab": [
{
"label": "mlab",
"provider": null,
"plan": "sandbox",
"name": "users",
"instance_name": "users",
"binding_name": null,
"credentials": {
"uri": "mongodb://CloudFoundry_someusergenerated:apasswordgeneratedautomatically#somehost.mlab.com:someport/CloudFoundry_database_name"
}
}
]
}
},
"application_env_json": {
"VCAP_APPLICATION": {
"cf_api": "https://donotuseapi.run.pivotal.io",
"application_name": "website",
"application_uris": [
"xxx.cfapps.io"
],
"name": "website",
"space_name": "space1",
"uris": [
"xxx.cfapps.io"
]
}
}
}
The connection with the database works fine with this default user and password. In order to get the mongodb uri from the environment variables, I am using npm package cfenv
const appEnv = require('cfenv').getAppEnv();
const env = process.env;
keys = {
mongodb: {
dbURI: appEnv.getServiceURL(env.MONGO_SERVICE_NAME)
}
};
In my manifest.yaml file I have this MONGO_SERVICE_NAME specified accordingly with the service name inside the environment variables.
---
applications:
- name: website
memory: 128M
disk_quota: 256M
random-route: true
buildpack: nodejs_buildpack
health-check-type: port
env:
MONGO_SERVICE_NAME: 'users'
Again, the db connection works fine.
===
Then I opened mLab website for this particular database and created a new database user.
Now I want to update the credentials.uri from VCAP_SERVICES (environment variables) for this particular service to use the new user and password.
As far as I coould see, cf update-service CLI command is not meant by that so I am wondering if this is a limitation from Cloud Foundry, Pivotal or mLab. I could bet that this limitation is due to the fact I am using Pivotal trial account and mLab free plan, however my question still the same if I upgrade plans.
Thanks,

Answer 1

As a user, it's not possible for you to change VCAP_SERVICES entries that are generated by a service brokers. These are fixed and not possible to change.
If you cf create-service'd a service, then it was created by a service broker and you get exactly what the service provider gives you. As was mentioned in the comments, depending on the service broker you may be able to pass arguments to the broker with cf create-service -c. Check the documentation of your service provider to see if there is an option to influence the credentials generated in the way that you would like.
If your service provider does not provide options to do what you want, you can create a service key instead of binding your service to an app. This will give you a set of credentials to your service that will last for the duration of the service key. The service key credentials are not automatically passed into an app, but you can feed them into your app in a variety of ways.
You can pass them in through environment variables.
You can create a user provided service (cf cups).
You can pass them through in application config or through a config server.
With all of these options, you are passing the credentials through to the app so you could in theory adjust or alter them before they get to your app.
Hope that helps!