Get CosmosDb Primary Connection String in ARM template

Question

I have an ARM template which sources the primaryMasterKey of a cosmosDb as follows:

{ "properties": { "enabled": true, "siteConfig": { "appSettings": [ { "name": "MongoDb:CnnDetails", "value": "[listKeys(resourceId('Microsoft.DocumentDB/databaseAccounts', variables('cosmosdb_full')), '2015-04-08').primaryMasterKey]" } }

How to I modify it to get the actual connection string instead?

I've tried couple of things:

1. changed the word primaryMasterKey to primaryConnectionString. This gives an error saying:

'The language expression property 'primaryConnectionString' doesn't exist, available properties are 'primaryMasterKey, secondaryMasterKey, primaryReadonlyMasterKey, secondaryReadonlyMasterKey'

2. changed the work listKeys to listConnectionStrings. This is red underlined in my visual studio, but seems to work when put through azure devops

'The language expression property 'primaryConnectionString' doesn't exist, available properties are 'connectionStrings'

3. I went to https://docs.microsoft.com/en-us/rest/api/cosmos-db-resource-provider/databaseaccounts/listconnectionstrings#code-try-0 to try it out. ListKeys returns a structure like this:

   { "primaryMasterKey": "[REDACTED]", "secondaryMasterKey": "[REDACTED]", "primaryReadonlyMasterKey": "[REDACTED]", "secondaryReadonlyMasterKey": "[REDACTED]" }

so I get why the .primaryMasterKey worked. But ListConnectionStrings returns:

{
  "connectionStrings": [
{
  "connectionString": "mongodb://[REDACTED]:10255/?ssl=true&replicaSet=globaldb",
  "description": "Primary MongoDB Connection String"
},
{
  "connectionString": "mongodb://[REDACTED]:10255/?ssl=true&replicaSet=globaldb",
  "description": "Secondary MongoDB Connection String"
},
{
  "connectionString": "mongodb://[REDACTED]:10255/?ssl=true&replicaSet=globaldb",
  "description": "Primary Read-Only MongoDB Connection String"
},
{
  "connectionString": "mongodb://[REDACTED]:10255/?ssl=true&replicaSet=globaldb",
  "description": "Secondary Read-Only MongoDB Connection String"
}
]
}

Not sure how to "index into it"?

Any clues gratefully received.

Answer 1

The answer here by oatsoda is correct but it will only work if you are within the same resource group as the Cosmos DB you are getting the connection string for. If you have the scenario where you Cosmos DB is in a different resource group to the resource you are generating an ARM template for the following snippet is what I have used to generate the connection string for an App Service and is working.

"Cosmos": {
   "value": "[listConnectionStrings(resourceId(parameters('cosmosResourceGroupName'),'Microsoft.DocumentDB/databaseAccounts', parameters('cosmosDbName')), '2019-12-12').connectionStrings[0].connectionString]",
   "type": "Custom"
}