Contents
data/authors/Paul Logan.json

App communication to Azure services from behind the corporate firewall

A tale of two offices

While developing an app for the first time that uses Azure Cosmos DB, I came across the situation where the app could connect to the Azure Cosmos DB service when working at home, but not while developing on the work office computer.

Cosmos DB Connection error
Microsoft.Azure.Cosmos.CosmosException : Response status code does not indicate success: ServiceUnavailable (503) Microsoft.Azure.Documents.TransportException: A client transport error occurred: The connection attempt timed out.

I immediately felt a sense of deja-vu.

On a previous app, I was using Azure Service Bus and came across the same issue - the connection was blocked when in the work office by the corporate firewall. When working at home, I was no longer behind the firewall.

The resolution back then was to configure the Service Bus client to use a different protocol and transport for communicating with Azure Service Bus.

Would there be a Cosmos DB version of the Service Bus client’s TransportType option?

A quick bit of Bing’ing lead me to the following Microsoft post about client connection modes:

If your application runs within a corporate network with strict firewall restrictions, gateway mode is the best choice because it uses the standard HTTPS port and a single DNS endpoint.

Without further ado, I updated my code while in the work office and the issue was immediately resolved.

	cosmoClient = new CosmosClient(connectionString: cosmoConnStr, new CosmosClientOptions
	{
		ConnectionMode = ConnectionMode.Gateway
	});

Cosmos DB Client

id property not defined

Unlike the Azure Data Table, a specific property called id needs to be part of the class definition.

This could be auto-generated, adding the option below, which will generate a GUID:

 new ItemRequestOptions { EnableAutomaticIdGeneration = true }

I am opting for an id that I will generate based on what will be the unique properties for each instance - in SQL world, a composite primary key.

Blog Warning
PartitionKey extracted from document doesn’t match the one specified in the header

https://stackoverflow.com/a/64124223/641165

Azure function not returning JSON to JS Fetch API