将NodeJS应用程序变量绑定到Pivotal Cloud Foundry Service

Question

I am looking to bind a PCF (Pivotal Cloud Foundry) Service to allow us to set certain api endpoints used by our UI within PCF environment. I want to use the values in this service to overwrite the values in the root directory file, 'config.json'. Are there any examples out there that accomplish this sort of thing?

Answer 1

The primary way to tackle this is to have your application do this parsing. Most (all?) programming languages give you the ability to load environment variables and to parse JSON. Using these capabilities, what you'd want to do is to read the VCAP_SERVICES environment variable and parse the JSON. This is where the platform will insert the information from your bound services. From there you, you have the configuration information so you can configure your app using the values from your bound service.

Manual Ex:

var vcap_services = JSON.parse(process.env.VCAP_SERVICES)

or you can use a library. There's a handy Node.js library called cfenv . You can read more about both of these options in the docs.

https://docs.cloudfoundry.org/buildpacks/node/node-service-bindings.html

If you cannot read the configuration inside of your application, perhaps there's a timing problem and you need the information before your app starts, you can use the platform's pre-runtime hooks.

https://docs.cloudfoundry.org/devguide/deploy-apps/deploy-app.html#profile

The runtime hooks allow your application to include a file called .profile which will execute before your application. The .profile file is a simple bash script which can do anything needed to ready your application to be run. The only catch is that this needs to happen very quickly because it must complete before your application is able to start up and your application has a finite amount of time to start (usually 60s).

In your case, you could use jq to parse you values and insert them info your config file, perhaps using sed to overwrite a template value. Another option would be to run a small Node.js script, since your app is using Node.js it should be available on the path when this script runs, to read the environment variables and generate your config file.

Hope that helps!