Episode 34 — Public and Private Endpoints Simplified
Welcome to Episode 34, Public and Private Endpoints Simplified, where we look at how applications expose themselves to the world or hide inside private networks. Endpoint choices decide who can reach a service, through which path, and under which guardrails. That means the decision shapes security, latency, and even how audits read your diagrams. A public doorway invites broad reach and fast onboarding, while a private doorway favors containment and predictable inspection. Neither is automatically better; each fits different risks and goals. In this episode we will translate platform features into plain decisions and show how names, routes, and policies work together. By the end, you will be able to choose an exposure pattern that matches your application’s sensitivity without tripping over complexity.
Public endpoints are addresses reachable from the internet, usually protected by authentication, encryption, and upstream defenses. They matter when users, partners, or devices cannot reasonably join your private network but still need access. Picture a customer portal, a public application programming interface, or a webhook target that must accept events from many sources. The risk is obvious: openness invites scanning and abuse, so you pair these endpoints with rate limits, application gateways, and a web application firewall. A common misconception is that transport layer encryption alone solves exposure; it only protects data in transit, not service behavior. Practical control includes strict allowlists for administration paths, staged rollout through deployment slots, and careful token lifetimes. When a service must be public, assume it will be probed every minute and design accordingly.
Private Link is the architecture that enables private endpoints, defining how consumers attach privately to providers within the same region or, in some cases, across approved scopes. The model separates two roles. A consuming virtual network creates a private endpoint, while the service exposes a private link resource that authorizes attachment. This matters because ownership and approval flow through explicit connections, giving you a ledger of who can talk to what. It also allows partner or multi-tenant scenarios where your customers reach your service privately without opening the internet. A misconception is assuming Private Link is just a fancy alias; it is a controlled mapping with lifecycle, access checks, and auditing. Treat it as a contract, not a shortcut. Clear approvals, naming, and tagging keep these contracts understandable at scale.
Service endpoints take a different path by extending your subnet’s identity to a platform service over the provider network while the service keeps its public address. The key benefit is that the service can allow your subnet explicitly and reject traffic from everywhere else. This reduces exposure compared to an open public endpoint, yet it does not create a private address inside your space. A helpful scenario is a storage account that should accept connections only from a specific application subnet, not the whole internet. A misconception is equating service endpoints with full privatization; packets still target a public endpoint, just through a trusted route. The model is simpler to adopt but provides weaker isolation than a private endpoint. Choose it when you need subnet-level control without DNS changes.
Comparing service endpoints and Private Link comes down to isolation strength, operational effort, and feature fit. Service endpoints are lighter weight, quick to enable, and often enough when the goal is to restrict access to selected subnets. Private Link is heavier to plan, because it consumes private addresses and demands name resolution changes, but it provides stronger isolation by removing public dependency. A useful rule of thumb is this: if auditors or regulations require that a platform service be inaccessible from the internet, Private Link is the safer choice. If your aim is simpler—only let these subnets talk—service endpoints may suffice. Remember that cost, limits, and cross-region behavior differ. Write down the requirements before committing so you do not retrofit later.
Domain Name System, or D N S, is essential for private endpoints because names must resolve to private addresses for clients inside your networks. When you create a private endpoint, the platform can publish records into a private D N S zone that you link to your virtual networks. Clients then resolve the familiar service name to the private mapping, not the public one. A misconception is relying on local host files for quick tests and leaving them in place; that shortcut hides resolution problems and breaks automation. Practical steps include standardizing private zones, linking them to all relevant networks, and validating resolution from the actual hosts that call the service. If a client resolves the public address, it will miss your private path entirely. Correct names make private connectivity real.
Preventing data exfiltration is a core reason to adopt private connectivity, and policies help enforce intent consistently. You can require private endpoints for sensitive services, deny public network access on configured resources, and audit exceptions with a timeline to close gaps. Imagine a rule that storage accounts holding regulated data must disable public access and accept only private traffic from approved subnets. A misconception is treating policies as paperwork; they are effective guardrails that block drift during hurried deployments. Pair them with tagging for data classification, so enforcement aligns to risk, not guesswork. Over time, policy plus private connectivity turns best practice into the default path rather than a heroic effort.
Firewalls, network security groups, and routing continue to matter after you adopt private connectivity. A private endpoint still sits in a subnet and depends on rules that allow clients to reach it. Likewise, a central firewall can inspect egress before traffic hits the provider network, even when the destination resolves privately. A misconception is assuming a private address bypasses inspection or that default rules will just work. In practice, review effective security group rules, confirm route tables point egress through required inspection, and ensure your firewall knows how to reach private service prefixes. Balance is important: do not overconstrain outbound paths so much that name resolution succeeds but packets cannot flow. Trace one request end to end and write down each decision point.
Testing connectivity and name resolution should follow a steady method that mirrors real behavior. Start on the client host and resolve the service’s fully qualified name, confirming a private address appears. Next, test a simple connection to the service port, and only then test the application path that uses identity and encryption. If it fails, check network security group logs and firewall decisions, because denies often explain what code cannot. A misconception is testing only from an administrator workstation; the real test is from the compute that will run in production. Record commands, outputs, and timestamps so fixes become knowledge, not folklore. When teams rehearse this method, incidents shrink from mysteries to measurable steps.
Designing platform as a service without public exposure is both possible and practical when you combine private endpoints, private D N S, and controlled egress. Picture a web application behind an application gateway that calls databases and message services exclusively through private endpoints. Internet traffic reaches the gateway, not the backends. Identity manages access rather than static keys, and outbound calls from compute traverse a firewall that blocks unknown destinations. A misconception is that private designs must be slow to adopt; templates and landing zones can bake in these patterns so teams use them by default. The result is a service that feels local, scales globally, and keeps auditors calm.
Multi-tenant services and known limitations deserve attention before you standardize. Not every service supports private endpoints in every region, and some multi-tenant endpoints cannot be fully privatized. Diagnostic tools, third-party webhooks, or cross-tenant integrations may still require public reach. This does not mean abandoning private patterns; it means acknowledging exceptions and wrapping them with the right controls. A misconception is promising zero public exposure everywhere, which leads to brittle designs. Instead, document exceptions, place them behind application gateways or front doors with web application firewall protection, and keep tokens and scopes tight. Treat the remaining public edges as deliberate, well-guarded gates rather than accidental holes.
A decision guide anchored in security posture keeps choices simple under pressure. If a service hosts regulated or high-risk data, prefer Private Link and enforce private D N S, with public access disabled where supported. If a service is internal but not sensitive, service endpoints may be sufficient, especially for quick migrations. If the service must be public, front it with an application gateway or content delivery layer, enable a web application firewall, and lock administration paths behind private networks or conditional access. Evaluate operational effort honestly; choose the strongest control you can sustain. Revisit the decision as features and regulations evolve, because endpoint capabilities expand over time.
