Azure runs 95% of the Fortune 500, and Azure Functions is one of the cheaper, more useful pieces of it. It's serverless compute that runs your code when something happens: an HTTP request lands, a queue message shows up, a timer fires, a file gets dropped into Blob storage. You don't manage servers, you don't provision infrastructure, and you only pay for what actually runs.
The catch is that "serverless" doesn't mean "set it and forget it." Get the setup wrong and you'll see slow cold starts, weird intermittent failures, and a bill that surprises you at the end of the month. Get it right and it mostly disappears into the background, which is what you want.
Here are seven practices we lean on when helping customers get more out of Azure Functions.
1. Deploy from a package, not from files
Functions in a function app deploy together, so a sloppy deploy takes everything down with it. Use the run-from-package approach. It speeds up Azure Resource Manager deployments, avoids file-locking issues during the copy step, and often shaves time off cold starts.
Deployment slots are worth setting up if downtime matters. Stage to a slot, swap, and roll back if something goes sideways. And if you're not already on continuous deployment tied to source control, that's the next thing to fix.
2. Write functions with the right design principles
Good performance and availability come down to a few habits:
- Defensive functions. Assume bad input and handle it gracefully.
- Stateless functions. State belongs in storage, not in memory between invocations.
- Planned cross-function communication. Use durable functions or queues. Don't have functions call each other directly over HTTP.
- Short-running functions. Long jobs belong on durable functions or a different compute model.
Most production incidents we've seen with Azure Functions trace back to one of those four.
3. Pick the right hosting plan
Your hosting plan controls how the app scales, what resources each instance gets, and which advanced features you can use. There are three options:
- Consumption plan. Pay per execution, scales to zero. Good for traffic that comes in bursts or sits low most of the time.
- Premium plan. Pre-warmed instances, VNet integration, no cold starts. Better for steady traffic or anything that needs network isolation.
- Dedicated (App Service) plan. Runs on App Service VMs you're already paying for. Useful when you have leftover capacity.
Most customers start on Consumption and only move up when cold starts or networking become a real problem.
4. Get your storage configuration right
Every function app needs an Azure Storage account for Queue, Blob, and Table storage. The function host uses it for triggers, bindings, and internal bookkeeping. Misconfigure it and you'll see weird symptoms: failed triggers, slow startups, intermittent errors that don't show up in your function code.
A few things to check. Don't share one storage account across unrelated function apps. Keep the storage account in the same region as the function. Lock down access with managed identities wherever you can.
5. Organize your functions properly
How you group functions across function apps affects scaling, security, deployment, and performance. Stuff too many functions into one app and cold starts get slower and memory use creeps up. Split them too aggressively and you're managing dozens of apps for no good reason.
The Microsoft guidance is a decent starting point. Our rule of thumb: group functions that scale together and share dependencies, separate functions that have different security boundaries or release cadences.
6. Monitor with Application Insights
Azure Functions integrates with Application Insights out of the box. Turn it on. It collects logs, metrics, and dependency traces, and the live application map is genuinely useful when something is failing in production.
If you're not looking at it, you're guessing.
7. Lock down security from day one
Cloud security has to start with the code, not bolted on after launch. The App Service platform handles a lot of the underlying hardening (patching, compliance checks, encrypted management traffic, DDoS and threat protection), but the application layer is on you.
A short checklist:
- Patch new vulnerabilities as they're disclosed
- Keep secrets out of network traffic; use Key Vault and managed identities
- Encrypt traffic on App Service connectivity features
- Encrypt management tooling (Azure PowerShell, Azure CLI, REST APIs)
Most of the breaches we've helped customers clean up came from leaked secrets or unpatched dependencies, not platform weaknesses.
Azure Functions is a small piece of the wider Azure platform, but it's one of the easier places to either save or burn money depending on how you set it up.
