We spent hours debugging connectivity when the real issue was authentication.
Here is why identity failures masquerade as network failures.
The Error Message Lies
Your app cannot connect to Azure SQL.
The error says: “Connection timeout.”
You check:
- firewall rules
- network security groups
- VNET configuration
- DNS resolution
Everything looks correct.
The issue is not networking. It is identity.
The Managed Identity does not have permissions on the database.
But the error said “timeout,” not “access denied.”
We learned to distrust the first error message.
Private Endpoints Make It Worse
Private endpoints eliminate public internet access.
Traffic stays in your VNET.
That is good for security. It is terrible for debugging.
When something fails, you check networking first because:
- the resource only accepts private traffic
- DNS must resolve to the private IP
- NSG rules must allow the traffic
- the subnet must be configured correctly
You spend hours on networking.
Then you realize the Managed Identity was never granted access to the resource.
The connection never got far enough for the identity check to return a clear error.
It just timed out.
Managed Identity Authentication Happens Late
Network connection happens first.
Identity authentication happens after the connection is established.
If identity fails, the failure can look like:
- connection reset
- timeout
- SSL/TLS error
We had an app that could not connect to Key Vault.
The error was “TLS handshake failed.”
We checked certificates. We checked cipher suites. We checked TLS versions.
The issue was that the Managed Identity was not assigned a role on the Key Vault.
The connection failed during authentication, but it looked like a TLS problem.
DNS Failures Hide Identity Issues
If your app uses private DNS zones for Azure services, DNS must resolve correctly.
If DNS fails:
- the connection never starts
- no identity check happens
- the error is “name not resolved” or “timeout”
You fix DNS. Then you get an identity error.
But you already spent two hours debugging DNS.
We learned to check identity configuration even when DNS is the obvious problem.
Because fixing DNS just reveals the next issue.
Firewall Rules Allow, But Identity Denies
Storage Accounts and Key Vaults have network firewalls.
If your app is allowed by the firewall, the network connection succeeds.
Then identity checks happen.
If the identity does not have the right role, access is denied.
But by then, you already verified networking works.
You assume the issue must be something else.
It is not. It is still identity.
We had a Storage Account that allowed traffic from a specific subnet.
An app in that subnet could not access blobs.
We checked:
- NSG rules (correct)
- firewall rules (correct)
- private endpoint configuration (correct)
The Managed Identity did not have “Storage Blob Data Reader” role.
We added it. Everything worked.
Logs Do Not Always Tell You
Azure Activity Logs sometimes show network failures as the error.
You have to dig into application logs, or use Application Insights, to see the real cause.
We debugged a Function App that could not connect to Cosmos DB.
Activity Logs said: “Network error.”
Application Insights showed: “Unauthorized.”
Same failure. Different error depending on where you looked.
We now check multiple log sources before concluding anything.
How We Debug Now
When we see connection failures, we check identity first:
- Does the Managed Identity exist?
- Is it enabled?
- Does it have the correct role assignment on the target resource?
- Is there a deny assignment blocking it?
- Are there Conditional Access policies affecting it?
Then we check networking:
- Does DNS resolve to the correct IP?
- Are NSG rules allowing traffic?
- Are firewall rules configured?
- Is the private endpoint working?
This order saves time.
Most connection failures in Azure are identity issues that look like network issues.
The Lesson
Azure networking and identity are tightly coupled.
A failure in one often surfaces as an error in the other.
Error messages are not always accurate.
Timeouts can mean:
- identity failure
- network failure
- DNS failure
- firewall block
- misconfigured private endpoint
You have to check all of them.
We learned to treat “connection timeout” as an identity problem first, and a network problem second.
That flipped our debugging process.
And it cut our mean time to resolution in half.