## Define route identifiers
First, define your application routes in your project's routing configuration, within `.upsun/config.yaml`. Here's a basic example:
```yaml {filename=".upsun/config.yaml"} theme={null}
routes:
"https://api.{all}/":
type: upstream
upstream: "api:http"
"https://{all}/":
type: upstream
upstream: "next:http"
```
To easily reference these routes later, add an `id` attribute to each one. Choose a meaningful string for the ID. Using the application name often works well:
```yaml {filename=".upsun/config.yaml",linenos=table,hl_lines=["5","9"],linenostart=1} theme={null}
routes:
"https://api.{all}/":
type: upstream
upstream: "api:http"
id: api # Identifier for the API route
"https://{all}/":
type: upstream
upstream: "next:http"
id: next # Identifier for the Next.js frontend route
```
Read the full Upsun documentation on [Route identifiers](https://docs.upsun.com/define-routes.html#route-identifiers).
## Fetch specific URIs from `$PLATFORM_ROUTES`
After deploying these changes, connect to one of your application containers using the Upsun CLI. For example, use `upsun ssh -A api` where `api` is your application's name. Inside the container, you can view the `PLATFORM_ROUTES` variable:
```bash {filename="Terminal"} theme={null}
web@api.0:~$ echo $PLATFORM_ROUTES
eyJodHRwOi8vYXBpLm1haW4tYnZ4ZWE2aS1yY...........
```
The output is a base64 encoded JSON string. To see the actual JSON content, you need to decode it:
```bash {filename="Terminal"} theme={null}
web@api.0:~$ echo $PLATFORM_ROUTES | base64 --decode
{"http://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {"id": null, "original_url": "http://api.{all}/", "primary": false, "production_url": "http://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "to": "https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "type": "redirect"}, "http://main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {"attributes": {}, "id": null, "original_url": "http://{all}/", "primary": false, "production_url": "http://main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "to": "https://main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "type": "redirect"}, "https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {"attributes": {}, "id": "api", "original_url": "https://api.{all}/", "primary": true, "production_url": "https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "type": "upstream", "upstream": "api"}, "https://main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {"attributes": {}, "id": "next", "original_url": "https://{all}/", "primary": false, "production_url": "https://main-bvxea6i-abcdefgh.ca-1.platformsh.site/", "type": "upstream", "upstream": "next"}}
```
You can make this JSON easier to read by piping it through `jq`. `jq` is a command-line tool for processing JSON data. It helps you parse, filter, and transform JSON, which is useful when working with APIs and configuration files. You can find more information on the [jq website](https://jqlang.org/).
***
```bash {filename="Terminal"} theme={null}
web@api.0:~$ echo $PLATFORM_ROUTES | base64 --decode | jq
{
"http://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {
"id": null,
"original_url": "http://api.{all}/",
"primary": false,
"production_url": "http://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/",
"to": "https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/",
"type": "redirect"
},
"http://main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {
"attributes": {},
...
},
"https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {
"attributes": {},
"id": "api",
...
},
"https://main-bvxea6i-abcdefgh.ca-1.platformsh.site/": {
"attributes": {},
"id": "next",
...
}
}
```
That's much better!
Now, you need a `jq` query to extract the specific URI you want, using the route `id` defined earlier. Here's how you can select the URI associated with the `id` "api":
```bash {filename="Terminal"} theme={null}
web@api.0:~$ echo $PLATFORM_ROUTES | base64 --decode | jq -r 'to_entries[] | select(.value.id=="api") | .key'
https://api.main-bvxea6i-abcdefgh.ca-1.platformsh.site/
```
Here's how that `jq` query works:
*(You can experiment with this query and the example JSON using the [online jq playground](https://play.jqlang.org/s/MWvtpbqG5ExfBgB).)*
1. `to_entries[]`: Converts the JSON object into an array where each item has a `key` (the URI) and a `value` (the route details object). The `[]` processes each item in the array.
2. `select(.value.id=="api")`: Filters these items, keeping only those where the `id` field inside the `value` object equals `"api"`. Change `"api"` to the route ID you need.
3. `.key`: Extracts the `key` field (the URI) from the filtered item.
4. The `-r` flag tells `jq` to output the raw value instead of its JSON representation.
Now you know how to get a specific URI. The next step is making this URI available to your applications as an environment variable.
## Set up environment variables using `.environment`
Upsun lets you define environment variables dynamically during the build process. You do this using a special script file named `.environment` placed in your application's source code directory. Find more details in the [documentation on setting variables via script](https://docs.upsun.com/development/variables/set-variables.html#set-variables-via-script).
Suppose your Next.js application needs an `API_HOST` variable with the API's URI. And your API application needs a `NEXT_PUBLIC_BASE_URL` variable with the frontend's URI. You can create a `.environment` file using the `jq` queries from the previous step.