Common Challenges With Tightly Coupled Systems in AWS

→ 𝐌𝐢𝐜𝐫𝐨𝐬𝐞𝐫𝐯𝐢𝐜𝐞𝐬 𝐀𝐧𝐭𝐢 𝐏𝐚𝐭𝐭𝐞𝐫𝐧𝐬 𝐓𝐡𝐚𝐭 𝐐𝐮𝐢𝐞𝐭𝐥𝐲 𝐁𝐫𝐞𝐚𝐤 𝐌𝐨𝐝𝐞𝐫𝐧 𝐒𝐲𝐬𝐭𝐞𝐦𝐬 Most microservices failures do not begin with outages. They begin with design choices that look harmless at first. Until scale exposes them. • 𝐒𝐞𝐫𝐯𝐢𝐜𝐞𝐬 𝐭𝐢𝐠𝐡𝐭𝐥𝐲 𝐜𝐨𝐮𝐩𝐥𝐞𝐝 Boundaries are weak. Teams lose deployment independence. One change starts impacting everything else. • 𝐃𝐢𝐬𝐭𝐫𝐢𝐛𝐮𝐭𝐞𝐝 𝐦𝐨𝐧𝐨𝐥𝐢𝐭𝐡 The system looks distributed on paper. In reality, services cannot evolve or deploy without depending on one another. • 𝐍𝐨 𝐀𝐏𝐈 𝐯𝐞𝐫𝐬𝐢𝐨𝐧𝐢𝐧𝐠 Even a small contract update can disrupt consumers. Backward compatibility protects trust across services. • 𝐓𝐨𝐨 𝐦𝐚𝐧𝐲 𝐦𝐢𝐜𝐫𝐨𝐬𝐞𝐫𝐯𝐢𝐜𝐞𝐬 Over splitting creates operational drag. More services do not always mean better architecture. • 𝐈𝐠𝐧𝐨𝐫𝐢𝐧𝐠 𝐝𝐚𝐭𝐚 𝐜𝐨𝐧𝐬𝐢𝐬𝐭𝐞𝐧𝐜𝐲 Without a clear consistency strategy, transactions become unreliable. This is where Sagas and eventual consistency matter. • 𝐒𝐲𝐧𝐜𝐡𝐫𝐨𝐧𝐨𝐮𝐬 𝐝𝐞𝐩𝐞𝐧𝐝𝐞𝐧𝐜𝐲 𝐜𝐡𝐚𝐢𝐧 Too many blocking calls create fragile service flows. One slowdown can trigger cascading failures. • 𝐍𝐨 𝐟𝐚𝐮𝐥𝐭 𝐢𝐬𝐨𝐥𝐚𝐭𝐢𝐨𝐧 A single failing component should not take down the rest of the platform. Isolation patterns improve resilience. • 𝐂𝐡𝐚𝐭𝐭𝐲 𝐜𝐨𝐦𝐦𝐮𝐧𝐢𝐜𝐚𝐭𝐢𝐨𝐧 Excessive service to service calls increase latency fast. Coarse grained APIs and async messaging reduce noise. • 𝐋𝐚𝐜𝐤 𝐨𝐟 𝐨𝐛𝐬𝐞𝐫𝐯𝐚𝐛𝐢𝐥𝐢𝐭𝐲 When logging, tracing, and metrics are weak, failures become harder to detect and fix. • 𝐒𝐡𝐚𝐫𝐞𝐝 𝐝𝐚𝐭𝐚𝐛𝐚𝐬𝐞 When multiple services use one database, ownership becomes blurry. Independent data boundaries preserve autonomy. • 𝐇𝐚𝐫𝐝𝐜𝐨𝐝𝐞𝐝 𝐜𝐨𝐧𝐟𝐢𝐠𝐮𝐫𝐚𝐭𝐢𝐨𝐧 If every config change needs redeployment, agility suffers. Externalized configuration supports faster adaptation. Microservices are powerful. But only when architecture decisions support clarity, resilience, and scale. Follow Umair Ahmad for more insights

The internet wobbled today. A DNS issue in a single AWS region cascaded across otherwise “safe” regions and availability zones. This was not just another regional outage. It was a practical lesson in the cloud's hidden, centralized dependencies. We build for multi-region resilience, but we are often betrayed by "global" services that are not as distributed as they appear. The gap between perceived autonomy and actual entanglement is where resilience fails. My lessons learned from today’s AWS outage: 1. The Control Plane Chokepoint AWS separates data planes (serving traffic) from control planes (the APIs managing resources). Many global control planes live in one region, often us-esst-1. When that hub is impaired, your automation fails. You cannot scale, deploy, or modify resources, even in perfectly healthy regions. 2. The Hidden Dependency Chain The obvious risk is your application failing. The hidden risk is the failure of a core service you do not directly use. Today’s DNS and networking issue rhymes with the 2020 Kinesis outage. A foundational service failed, and higher level systems like Cognito, Lambda, and Auto Scaling began to error simply because they relied on it internally. 3. The Myth of the "Island" Application Even a perfect multi-AZ application is not an island. It must resolve DNS, fetch IAM tokens, pull container images, and push logs. These core functions often rely on shared, centralized services. When those services choke, your redundant application times out. History provides a classic intelligence analog. During WWII, Allied planners knew German communications were heavily encrypted. But they also knew most signals could only transit a few central relay stations. By targeting those nodes, they could blind the entire network without breaking a single code. The cloud's core services are these modern relay stations. We are not just choosing between regional availability and multi-region reliability. We are choosing between apparent distribution and actual fault isolation. The core principle is to understand your actual blast radius. A system is only as resilient as its most critical, least visible dependency. Today is a reminder that resilience is not an architectural diagram. It is the verified, tested ability to withstand the failure of a dependency you probably forgot you had.

"We'll use events and CDC for loose coupling." This statement sounds good in a design doc. In reality, it's a top reason for "silent" production failures. An upstream system (Service A) produces data. A downstream system (Service B) needs that data. To avoid a "tight coupling," the engineer has Service B "listen" for changes from Service A. Maybe Service B uses Change Data Capture (CDC) to stream changes from Service A's database. Or it just consumes from a generic event log. Service A doesn't even know Service B exists. This feels like a win for loose coupling. It's actually a time bomb. And then reorg happens, team gets changed completely. The failure happens 3-6 months later. The team for Service A changes their data contract. They rename a field. They refactor the code and stop producing a specific event. Why? Because they forgot Service B was silently listening. The dependency was implicit. It wasn't obvious in their code. Service A's tests pass. They ship their change. Weeks later, Service B breaks. The data is corrupt. The system is down in production. The damage is done, and it takes days to trace and fix the problem, which happened due to a change made a month ago. That's why, stop relying on silent event streams for critical data flows. Use an explicit command instead. This doesn't mean it must be a synchronous API call. It can (and often should) still be an event. But Service A must explicitly publish a well-defined event. The code in Service A should literally say: event_publisher.send("OrderProcessed_v1", data) Now, the dependency is explicit. When the Service A team refactors their code, they see this line. They can't forget it. They are forced to think: "Who consumes OrderProcessed_v1? Oh, Service B. We are moving to v2, so we need to tell them." This conversation happens during development. Not during a production fire. Don't confuse "loose coupling" with "implicit dependencies." One is a good design goal. The other is a production incident waiting to happen. If you are preparing for mid-senior/staff SDE, EM system design HLD interviews, and need help, DM me COACH.

𝗛𝗼𝘄 𝗰𝗼𝘂𝗽𝗹𝗶𝗻𝗴 𝗸𝗶𝗹𝗹𝘀 𝘀𝗰𝗮𝗹𝗮𝗯𝗶𝗹𝗶𝘁𝘆 𝗶𝗻 𝗺𝗶𝗰𝗿𝗼𝘀𝗲𝗿𝘃𝗶𝗰𝗲 𝗮𝗿𝗰𝗵𝗶𝘁𝗲𝗰𝘁𝘂𝗿𝗲 Imagine joining a project with 𝟔+ 𝐦𝐢𝐜𝐫𝐨𝐬𝐞𝐫𝐯𝐢𝐜𝐞𝐬 … Everything looks 𝐜𝐥𝐞𝐚𝐧 𝐚𝐧𝐝 𝐨𝐫𝐠𝐚𝐧𝐢𝐳𝐞𝐝, 𝐞𝐚𝐜𝐡 𝐬𝐞𝐫𝐯𝐢𝐜𝐞 𝐡𝐚𝐬 𝐚 𝐧𝐚𝐦𝐞, 𝐚 𝐑𝐄𝐀𝐃𝐌 𝐟𝐢𝐥𝐞, 𝐞𝐯𝐞𝐧 𝐚 𝐃𝐨𝐜𝐤𝐞𝐫𝐟𝐢𝐥𝐞. You think: “𝑻𝒉𝒊𝒔 𝒊𝒔 𝒎𝒐𝒅𝒆𝒓𝒏, 𝒔𝒄𝒂𝒍𝒂𝒃𝒍𝒆, 𝒓𝒆𝒔𝒊𝒍𝒊𝒆𝒏𝒕…” But the moment you try to scale just one service? Surprise.. Service A calls B, B calls C, C calls D… Each one waiting on the next, Each one nested in retries. So you want to scale A? Guess what , you have to scale half the system with it. 𝐀𝐧𝐝 𝐭𝐡𝐚𝐭’𝐬 𝐰𝐡𝐞𝐧 𝐲𝐨𝐮 𝐫𝐞𝐚𝐥𝐢𝐳𝐞: Microservices aren't about how many services you have… They’re about how independent they are from each other. 𝗪𝗵𝗮𝘁 𝗱𝗼 𝘆𝗼𝘂 𝗮𝗰𝘁𝘂𝗮𝗹𝗹𝘆 𝗳𝗶𝗻𝗱? 🔹A system that’s tightly coupled 🔹Blocking calls everywhere 🔹Latency coming from an endless chain 🔹Retry on top of retry = you're creating pressure on yourself 𝗦𝗼 𝘄𝗵𝗮𝘁 𝗱𝗼 𝘆𝗼𝘂 𝗱𝗼? 🔸Shield the clients with an 𝐀𝐏𝐈 𝐆𝐚𝐭𝐞𝐰𝐚𝐲 No more clients talking to 𝟔 𝐬𝐞𝐫𝐯𝐢𝐜𝐞𝐬 to complete one request. The gateway 𝐡𝐚𝐧𝐝𝐥𝐞𝐬 𝐫𝐨𝐮𝐭𝐢𝐧𝐠, 𝐚𝐮𝐭𝐡, 𝐜𝐚𝐜𝐡𝐢𝐧𝐠, everything is centralized. 🔸 Build an 𝐎𝐫𝐜𝐡𝐞𝐬𝐭𝐫𝐚𝐭𝐨𝐫 𝐒𝐞𝐫𝐯𝐢𝐜𝐞 Control service calls: 𝐨𝐫𝐝𝐞𝐫, 𝐜𝐨𝐧𝐝𝐢𝐭𝐢𝐨𝐧𝐬 𝐚𝐧𝐝 𝐫𝐞𝐝𝐮𝐜𝐞 𝐭𝐡𝐞 𝐜𝐨𝐮𝐩𝐥𝐢𝐧𝐠 𝐚𝐬 𝐦𝐮𝐜𝐡 𝐚𝐬 𝐩𝐨𝐬𝐬𝐢𝐛𝐥𝐞. 🔸Bring in 𝐀𝐬𝐲𝐧𝐜 𝐌𝐞𝐬𝐬𝐚𝐠𝐢𝐧𝐠 𝐰𝐢𝐭𝐡 𝐑𝐚𝐛𝐛𝐢𝐭𝐌𝐐/𝐊𝐚𝐟𝐤𝐚, no more waiting, each service sends a message and moves on. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: instead of A calling B and waiting, 𝐀 𝐞𝐦𝐢𝐭𝐬 𝐚𝐧 𝐞𝐯𝐞𝐧𝐭 𝐥𝐢𝐤𝐞 "𝐎𝐫𝐝𝐞𝐫𝐏𝐥𝐚𝐜𝐞𝐝" B listens and does its work 𝐨𝐧𝐥𝐲 𝐰𝐡𝐞𝐧 𝐭𝐡𝐞 𝐞𝐯𝐞𝐧𝐭 𝐚𝐫𝐫𝐢𝐯𝐞𝐬. 🔸Add 𝐎𝐛𝐬𝐞𝐫𝐯𝐚𝐛𝐢𝐥𝐢𝐭𝐲 𝐰𝐢𝐭𝐡 𝐎𝐩𝐞𝐧𝐓𝐞𝐥𝐞𝐦𝐞𝐭𝐫𝐲 No guessing. Trace everything: From the initial request to the final service. See latency, failures and bottlenecks in real time. 𝗟𝗲𝘀𝘀𝗼𝗻 𝗹𝗲𝗮𝗿𝗻𝗲𝗱 : 👉 Microservices that are tightly coupled = just a monolith in disguise. 👉 Want to scale? You need decoupling. 👉 Want resilience? You need async and observability. 👉 Want control? You need clear abstraction and boundaries. 𝗧𝗵𝗶𝗻𝗸 𝗮𝗯𝗼𝘂𝘁 𝗶𝘁: If every service is afraid to change… You're not in a distributed system. You're in distributed fear. #Microservices #DevOps #Architecture #Scalability #SystemDesign #SoftwareEngineering #CloudComputing #Async #Observability #TechTips

Amazon’s official postmortem, https://lnkd.in/giuwe2VY, on the us-east-1 outage reads like a deep dive into how fragile control planes can be when automation meets scale. A single race condition in DynamoDB’s DNS automation spiraled into EC2 launch failures, Lambda throttling, and NLB health-check chaos cascading across nearly every dependent service. It’s not that AWS is unreliable; it’s that our architectures are too tightly coupled to vendor control planes. When DNS, orchestration, and routing all depend on the same automation layer, “multi-AZ” isn’t the same as resilient. Here are a few lessons from the postmortem worth carrying forward 👇 DNS isn’t invincible. Independent DNS and health checks give you a fallback path when a provider’s control plane falters. Compute orchestration can fail noisily. Design workloads to recover even when new capacity can’t launch. Health checks can amplify failure. Add damping, delay, and edge-managed routing to avoid self-inflicted downtime. Dependencies cascade. The weakest link isn’t your app; it’s the invisible systems you assume “just work.” This outage reminded us that resilience isn’t just about redundancy, it’s about decoupling. I pulled together an Engineering Checklist for Control-Plane Resilience to help teams assess how exposed they are to these same failure patterns. Comment AWS and I’ll share the doc.