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Originally published at malaymehta.com The Interview Trap If you look at most system design tutorials, you get an extreme use case. Design Twitter. Design YouTube. Scale it to a billion users. Draw boxes on a whiteboard for 45 minutes. Do you think your app will be used by a billion users on day one? The answer is almost always no. But the tutorials don't teach you what to do when you have 500 users, unclear requirements, a team of four, and a quarter to ship something that works. Real system design is nothing like a whiteboard interview. You don't get clean requirements, you don't design from scratch, and nobody asks you to handle a billion requests per second on day one. Real System Design Starts with Questions, Not Diagrams The very first thing that matters in system design is something most tutorials skip entirely: unclear and chaotic requirements. In the real world, requirements don't come as a clean problem statement. They come from non-technical business teams, and you need to navigate through cross-questions to get all the clarity you need. Ask as many questions as possible. Understand your functional and non-functional requirements. Which features need to be synchronous and which can be async? What are the read and write load patterns? What is the maximum and average number of concurrent users right now? What does authentication look like? Do you need role-based access control? These questions drive your choices. You don't always need an axe where a knife will do. Being minimalist with a reasonable growth prediction and a 3, 6, 9 month plan will take you in the right direction. There will be things the situation demands immediately but would take more time than expected. Taking a predictable hit now and fixing it at the right future time without missing that balance is truly important. Weighing what will be expensive to change later, in terms of dollar cost or human effort, is how real architectural decisions get made. Pushing Back on Bad Requirements Many

Slack has outlined how its AI serving infrastructure evolved through four distinct phases, moving from a self-managed Amazon SageMaker deployment to a multi-cloud architecture spanning AWS Bedrock and Google Cloud Vertex AI. By Matt Foster

Backed by Mayfield and Aramco Ventures, Vishal Sikka’s new venture brings together veterans from SAP, Infosys, and VianAI.

Recently, we encountered a case on a RHEL 9 machine where an RPM query did not show any information about installed package even though the package files were present in the filesystem. Although RPM reported that the package was not installed, I was still able to run tcpdumpcommand and use it without any issues. The binary was present there in the filesystem and I was able to run it successfully. Fixing RPM Database Desynchronization on RHEL - bidhankhatri.com.np Recently, we encountered a case on a RHEL 9 machine where an RPM query did not show any information about installed package even though the package files were present in the filesystem. bidhankhatri.com.np

The safety board, known for its thorough investigations, is probing the crash alongside the National Highway Traffic Safety Administration.

When designing systems like Facebook, WhatsApp, Netflix, Amazon, or Instagram, one of the first questions a system designer asks is: Can a single server handle the traffic? How much storage will be needed? Do we need caching? How much RAM should our cache have? How many servers should we deploy? Before discussing databases, load balancers, microservices, or caching layers, we need a rough understanding of the scale. This is where Back-of-the-Envelope Calculations come into the picture. Why Do We Need Back-of-the-Envelope Calculations? Imagine you're asked to design Facebook. If you immediately start drawing: Load Balancer ↓ Application Servers ↓ Redis Cache ↓ Database without knowing the expected traffic, you're designing blindly. System design is fundamentally about making trade-offs. To make those trade-offs, we first need estimates. Back-of-the-envelope calculations help us answer: How much traffic will the system receive? How much data will be generated? How much cache memory is required? How many servers are needed? The numbers don't need to be perfect. They only need to be close enough to make architectural decisions. What Exactly Is a Back-of-the-Envelope Calculation? A quick estimation technique used to approximate: Traffic Storage Memory Server Capacity using rough assumptions. Think of it as: "Getting the order of magnitude correct rather than getting the exact number correct." A system designer rarely needs perfect accuracy during interviews. They need reasonable estimates. The Standard Estimation Flow Whenever you get a System Design question: Users ↓ Traffic ↓ Storage ↓ RAM / Cache ↓ Number of Servers ↓ Architecture Design Always estimate first. Design later. The Ultimate Estimation Cheat Sheet Storage Units Unit Value 1 KB 10³ Bytes 1 MB 10⁶ Bytes 1 GB 10⁹ Bytes 1 TB 10¹² Bytes 1 PB 10¹⁵ Bytes Time Units Unit Value 1 Minute 60 Seconds 1 Hour 3600 Seconds 1 Day 86,400 Seconds Common Assumptions Metric Approximation Peak Traffic 3× Average Traffic Active

Synchronous billing is easy, and that's the problem — it makes you think all billing is easy. When a request does its work inline, the billable number is in the response by the time you send it. The gateway meters from there — the meter write, retries and all, is its problem, not yours. From your side, synchronous billing is one number in the response. Asynchronous work breaks that. The request submits a job; the work happens later, in a worker; the result comes back through a poll or a callback. And the thing you bill for — characters processed, pages converted — isn't known when the request arrives. It's known when the job finishes . So you can't meter at the edge. The meter has to fire from the completion path. And the real difficulty is firing it exactly once per unit of completed work — because requests, polls, and retries all conspire to make that zero times or many times. This is platform-agnostic. Every submit-process-poll API has it. I'll use the system I run as the example, but the shape is the same anywhere. Three ways metering goes wrong On arrival. Carry the synchronous habit over and you meter when the job is submitted. But you don't know the size yet, so you're forced into a crude flat fee — or you bill for work that hasn't happened and might fail. Wrong unit, wrong time. On retrieval. The subtle one. You wire the meter to fire when the client fetches the result. Now a client who submits a job, lets it run — costing you real money downstream — and never bothers to poll is never billed. You did the work for free. "Completion" is not "the client picked up the result." It's the worker finishing. Without a fixed quantity. Input characters or output characters? Pages before OCR or after? If you haven't decided exactly what you measure and where, invoices drift and customers argue. Decide once; measure there. All three point the same way: meter on measured work-completion, with a fixed definition of the unit. Not on arrival. Not on retrieval. The mechanism:

Long-running workflows look simple when you first build them. Something happens. A few systems exchange data. Everything completes. Done. At least that's the expectation. Reality is very different. The biggest thing I underestimated was time. Not execution time. Elapsed time. Because once workflows start running for hours, days, or continuously, strange things start happening. APIs become temporarily unavailable Data changes halfway through the process Retries arrive much later than expected Someone manually updates a record Another system processes things in a different order Nothing is broken. But everything is slightly different from when the workflow started. Early on, I assumed workflows were transactions. Start. Execute. Finish. Now I think of them as conversations between systems. And conversations can get interrupted. Another thing I underestimated: State changes. You might start processing an order that is "pending". Ten minutes later, another system marks it as "cancelled". An hour later, a retry comes in from an earlier step. If your workflow only thinks about data, weird things happen. Because the world has changed while the process was still running. Long-running workflows also expose assumptions you didn't know you made. Like: this API will always respond quickly data will arrive in order users won't modify records manually retries will happen immediately Those assumptions survive in testing. Production removes them quickly. One thing that changed how I build these systems: I stopped asking: "Will this workflow finish?" And started asking: "What state will the world be in when it finishes?" Because those are two very different questions. Most problems in long-running systems aren't caused by one big failure. They're caused by lots of small changes happening while the workflow is still alive. And if you don't account for that, eventually the workflow finishes successfully and still produces the wrong outcome. This is something we think about constantly

Introduction This is the second part of sharing my journey to create a microservices-based backend system, in the previous part, I introduced the system and its services. In this part I am going to mention the main things that happened with me from then until now. Transitioning to online DBaaS platforms The first main thing was to transition my databases from my local device to accessible over the internet. I used Neon and MongoDB Atlas . Although performance-wise it is better to deploy the database on the same server that the whole system so all services can access the databases without network overhead , This solution is better from a point, that is avoiding consuming the free VM instance that I got to host my main services, as with DBaaS platforms I will not require storage for databases or additional overhead to handle the DBMS on a free small resources-constrained VM. Observability Observability is one of the main concerns in any system, it gives the ability for the system to expose what happens inside it without any need to guess and manually trace the code to determine where the error may happened. I utilized OpenTelemetry , as I found it is most used and accepted tool to log, trace and collect metrics about the system and the traffic. Also, I loved that it is not related to specific framework, that is .NET by the way, I loved the idea that it is standalone tool. But logging and tracing and metrics collection will not be beneficial if we do not see it actually and can achieve monitoring from those telemetry data, so I used Grafana Cloud to export the telemetry data to some place that is accessible online and a tool that can generate dashboards and visualizing for the metrics ( Prometheus ), and UI that can show all the telemetry data easily. Deployment Until this point, we have a system that is fully functional and have consistent docker configuration for its services via Docker Compose, and it database is already there and available. Now this is the point at

Payment data pipelines fail in ways that ruin a payments engineer’s week, and the failures rhyme. The dashboards froze. Fraud scores arrived after the transaction had already cleared. Settlement reports came in stale. Nobody slept. The frustrating part is that the same data architecture had run fine for years. So, what changed? The honest answer is that batch thinking does not survive contact with real-time payments. A lot of banks built their data foundations in an era when nightly jobs were good enough. Load the warehouse overnight, run the reports in the morning, move on. That rhythm worked when money moved slowly. It does not work when a customer expects an instant confirmation and a fraud engine has milliseconds to make a call. Here is where things crack. Real-time payment rails push a constant stream of events instead of a tidy nightly dump. Your pipeline now has to ingest, transform, and serve data while transactions are still happening. Add ISO 20022 into the mix and the pressure climbs. ISO 20022 messages are rich. They carry far more structured detail than the old formats, which is wonderful for analytics and miserable for a pipeline that was never designed to parse that much context at speed. This is not a fringe concern either. Swift reported that by the time its MT/ISO 20022 coexistence period closed in November 2025, around 80% of daily traffic was already running on the ISO 20022 format, with more than 3.1 million of these messages exchanged every day. The rich-data era is the default now, not the roadmap. Then there is the fraud-scoring window. Fraud models need fresh features. Account behaviour over the last few minutes, velocity checks, device signals. If your pipeline takes thirty seconds to surface that data, the fraud decision is already too late. You are essentially detecting fraud after the loss. That gap between when data is created and when it becomes usable is the silent killer in most payment systems. And the cost of getting it wrong runs

If your LLM costs are climbing, the instinct is almost always the same: swap to a cheaper model. GPT-4 to GPT-4-mini. Claude Opus to Claude Haiku. Sometimes that helps a little. It rarely fixes the actual problem. The actual problem, in most workflows I've looked at, is that every step gets routed through the LLM, even the steps that don't need language reasoning at all. This post breaks down a simple mental model for deciding what should and shouldn't touch an LLM, with a working example you can adapt. The four components of any AI workflow Every automated workflow — whether it's a support ticket router, a fraud check, or a content pipeline — is built from some combination of four building blocks. They get treated the same once a workflow diagram is drawn flat, but they have wildly different cost and latency profiles. Component What it does Think of it as Typical cost Trigger Starts the workflow The doorbell ~$0 Deterministic ML Structured predictions — classify, score, rank The calculator Cents per 1,000 calls LLM / Generative Reads, writes, reasons in language The writer Dollars per 1,000 calls Tool / API Fetches or writes real data The hands Cents per 1,000 calls The gap between row 2 and row 3 is the whole article. A classifier and an LLM call can solve the exact same problem, but one costs roughly 100-1000x more than the other, depending on model and provider. If you're not deliberately deciding which one handles which step, you're probably defaulting to the expensive one — because in frameworks like LangChain or a quick custom agent loop, it's just easier to shove everything into a prompt. Where this actually shows up Here's a workflow I see constantly: an automated support ticket triage system. flowchart LR A[New support ticket] --> B{Classify intent} B --> C[Route to team] B --> D[Auto-draft response] D --> E[Update CRM] A naive build sends the entire ticket text to an LLM and asks it to do everything at once: classify the intent, decide routing, draft a re

Good architecture is not only about how a system is built. It is also about how well the team can understand that system once it is running. That is where observability belongs in the architecture conversation. It is common for observability to be treated as something that comes after the main engineering work. The service gets built. The API works. The deployment succeeds. Then, somewhere near the end, the team starts thinking about logs, dashboards, alerts, and operational visibility. That approach creates a gap. The architecture may look clean on paper, but once the system is in production, the team has to understand how it behaves under real conditions. Real users do not follow the happy path perfectly. Dependencies slow down. Queues back up. Data arrives in unexpected shapes. Deployments change behavior in ways that are not always obvious. If the system does not give the team a way to see those things clearly, the architecture is incomplete. Observability is not decoration around the system. It is part of the system design. Architecture Describes the System. Observability Shows the Truth. Architecture is built on assumptions. During design, teams make reasonable guesses about usage patterns, service boundaries, dependency behavior, data flow, scale, latency, and failure modes. Some of those assumptions are based on experience. Some are based on current requirements. Some are simply the best call the team can make with the information available at the time. That is normal. The problem is not that architecture contains assumptions. Every architecture does. The problem is when those assumptions cannot be tested once the system is real. A design might assume that an external dependency will be reliable enough. Production may show that it is the slowest part of the request path. A queue might look like a clean decoupling point during design. Production may reveal retry behavior, duplication, or ordering concerns that were not obvious upfront. A serverless function m

The Problem: Feature Velocity Was Creating Structural Debt The system originally started as a simple feature delivery backend: A Django API powering agricultural insights Celery workers handling asynchronous processing Independent endpoints for each new capability A growing set of Earth Observation computations (NDVI, NDWI, etc.) At first, it worked. But as more features were added, a pattern emerged: Each feature introduced its own pipeline logic Observability was inconsistent across services API contracts drifted between frontend and backend Debugging required tracing multiple disconnected systems We weren’t scaling functionality. We were scaling fragmentation. The Turning Point: Features vs Platforms The key realization was simple: Features solve user problems. Platforms solve system problems. We were repeatedly rebuilding: Authentication flows Data ingestion logic Processing pipelines API validation layers Monitoring hooks Each feature was solving its own version of these concerns. That is where platform engineering became necessary. The Shift: Introducing a Platform Layer We introduced a platform layer between feature delivery and infrastructure. Instead of building isolated pipelines, we standardized: 1. Unified API Surface All Earth Observation workflows (NDVI, NDWI, and future indices) were normalized into a consistent API contract. Shared request/response structure Versioned endpoints Schema validation through serializers Central routing logic This eliminated endpoint fragmentation. 2. Standardized Processing Pipeline Celery tasks were refactored into a reusable pipeline pattern: Ingestion Validation Computation Storage Publishing Instead of feature-specific workers, we moved toward composable tasks. This allowed new indices or processing logic to plug into the same execution flow. 3. Observability as a First-Class Layer One of the biggest failures in the original system was visibility. We introduced: Structured logging across all services Traceable job IDs

I bombed a system design interview last year — not because I didn't know the architecture, but because I spent the first 5 minutes fighting Excalidraw. So I built SystemDesignBoard — a free, keyboard-first whiteboard specifically for system design interviews. What it does You open it, press a key, and start drawing. No account, no onboarding, no drag-from-a-sidebar friction. R → place a Service node C → place a Database/Cache/Queue A → connect two nodes N → open the scratchpad for scale math The features I'm most proud of Animated connectors that show communication type Instead of just drawing arrows, connectors visually encode how services talk: ⇄ sync — paired dashes (request + ACK) ≋ stream — near-solid fast line with glow (continuous pipeline) This matters in interviews — your interviewer can glance at your diagram and immediately understand the communication pattern. Cloud provider badges Tag any node as AWS (EC2, Lambda, RDS, S3), GCP (GKE, Cloud Run, Firestore), or Azure. Each subtype has its own icon. Trade-off logging Right-click any node → Log Trade-offs → attach your CAP theorem stance, consistency level, and scaling strategy directly to the component. Diagram-as-Code Type: [Mobile App] -> [API Gateway] [API Gateway] -> [Auth Service] [Auth Service] -> [Users DB] [Feed Service] -> [Posts DB x3] [Feed Service] -> [Redis Cache] Hit Apply — it auto-lays out the whole architecture in seconds. Export to animated GIF Export your diagram as a GIF that shows live traffic flow animations. Great for sharing after an interview or in a design doc. Tech stack React + TypeScript + Vite @xyflow/react (ReactFlow v12) for the canvas Zustand + Immer for state with full undo/redo html-to-image + gifshot for PNG/GIF export It's free and open No signup required. Works entirely in the browser. Free during beta. 👉 systemdesignboard.com Would love feedback — especially from anyone who's done system design interviews recently. What's missing? What's annoying? Drop a comment below

As software engineers, we often architect solutions in a virtual ideal: fast networks, elastic resources, and servers that never physically degrade. But what happens when your carefully crafted systems need to interact with the messy, unpredictable physical world? Think factory floor monitors, real estate camera networks, or remote tracking devices. Suddenly, those cloud assumptions about infinite uptime and perfect connectivity crumble. My journey, particularly architecting and maintaining a continuous 24/7 camera livestream for a real estate group over six years, has been a masterclass in this reality. It's revealed that true reliability in the physical realm demands a hybrid approach – one that intelligently merges the power of edge computing with the scalability and data insights of the cloud. This isn't just about connecting devices; it's about building resilience into the very fabric of your architecture. In this article, I'll share the battle-tested strategies and design principles that enable systems to not just survive, but thrive, despite the harsh realities of physical deployment. 1. The Core Strategy: Smart Edge, Simple Cloud One of the most common pitfalls in hybrid architecture design is treating the edge device as a mere 'dumb' terminal, solely responsible for streaming raw data to a powerful cloud backend. This approach creates a critical single point of failure: if the network drops, the entire system grinds to a halt. Instead, I advocate for a Smart Edge, Simple Cloud architecture. This principle establishes a clear division of responsibility: The Edge : This is where the magic happens locally. The edge system should be robust enough to handle local processing , data filtering , buffering , and immediate hardware control . Critically, it must be capable of operating autonomously for extended periods without an active cloud connection. Think of it as a mini data center, designed for self-sufficiency. Benefits of a Smart Edge : Reduced bandwidth cost

The Counterintuitive Truth: Feature Flags Are Not Config Files Most engineers first encounter feature flags as a simple abstraction: a key-value lookup that returns true or false. That mental model works fine for a single service handling a few hundred requests per minute. It becomes actively dangerous at scale. A mature feature flag system isn't a config file with an API wrapper — it's a distributed control plane . The distinction matters architecturally. A control plane manages the real-time behavior of a running system across many nodes simultaneously, with its own consistency guarantees, failure semantics, and propagation latency. That's a fundamentally different design problem than reading a YAML file on startup. One constraint drives every downstream decision: user traffic must never block on a remote flag service call. If evaluation requires a synchronous RPC, you've coupled your request path to the availability and latency of an external system. Netflix's Archaius library enforces this by evaluating flags entirely in-process against a locally-cached configuration snapshot. A network round-trip per evaluation injects 10–50ms of tail latency at p99 — catastrophic when you're competing on streaming start times measured in hundreds of milliseconds. Google, Meta, and Netflix collectively evaluate flags against millions of requests per second with sub-millisecond overhead. That figure is only achievable through local evaluation backed by an async synchronization layer, not RPC. The other failure mode engineers underestimate is flag sprawl . Systems accumulate flags the way codebases accumulate dead functions — gradually, then all at once. I've seen services carrying thousands of flags where fewer than 10% were actively managed. The operational weight alone becomes a liability: which flags are safe to remove? Which ones are kill switches for production behavior that no one documented? Knight Capital's $440M loss in 45 minutes in 2012 remains the canonical cautionar

Failures are obvious. Retries are sneaky. When something fails, everyone notices. An alert goes off. A request errors out. Someone starts investigating. Retries are different. They look harmless. Most of the time, they save the system. But sometimes, retries create bigger problems than the original failure. Imagine an API call times out. No problem. The system retries. But what if the first request actually succeeded and only the response was lost? Now the retry creates: duplicate orders repeated emails inconsistent records workflows running twice The failure happened once. The retry multiplied it. Another thing I've seen: One slow dependency causes requests to pile up. Retries start firing. Those retries create even more traffic. Which slows things down further. Which triggers even more retries. Suddenly, the system is spending more effort retrying than doing useful work. Retries also hide problems. A temporary issue gets retried five times and eventually succeeds. Everything looks normal. Meanwhile: latency increases queues grow users experience delays Nothing technically failed. But the system is getting less healthy. What changed for me is that I stopped treating retries as free. Every retry has a cost. It consumes resources. It increases load. And if actions aren't designed carefully, retries can repeat side effects that should only happen once. Now when I build something, I don't ask: "What happens if this fails?" I ask: "What happens if this runs again?" Because in production, things almost always run again. And if the answer is "bad things happen," the retry mechanism isn't helping. It's making things worse. Failures are part of every system. Retries are too. The difference is that failures usually happen once. Retries can turn one problem into hundreds if you don't design for them. This is something we think about constantly at BrainPack when operating long-running workflows across multiple systems. AI and automation layers make retries even more common, wh

Single-model systems are simple. Multi-model systems are powerful. The challenge isn't choosing models — it's designing the architecture that orchestrates them. A multi-model system isn't about having more models. It's about having the right model for the right task at the right time. Architecture patterns Five patterns cover most use cases: Pattern Complexity When to use Tradeoff Single Model Lowest Prototyping, simple tasks Limited capability Sequential Low Multi-step workflows Higher latency Parallel Medium Independent tasks Higher cost Hierarchical High Complex reasoning Complex orchestration Ensemble Highest Critical decisions Highest cost Pick the simplest one that works. Complexity is real, and it compounds. Sequential architecture Process tasks through a chain of models, each specializing in a step. Pattern 1: Pipeline Pipeline pattern — each model's output feeds the next: class ModelPipeline : def __init__ ( self ): self . models = [ { " model " : " qwen2.5-1.5b " , " task " : " classify " }, { " model " : " qwen2.5-7b " , " task " : " extract " }, { " model " : " qwen2.5-32b " , " task " : " reason " }, ] def process ( self , input : str ) -> str : current = input for model_config in self . models : current = self . call_model ( model_config [ " model " ], self . create_prompt ( model_config [ " task " ], current ) ) return current Latency adds up. Three models in sequence means three times the latency. Only use this when each step actually needs a different model. Pattern 2: Router Router pattern — classify the task, route to the specialist: class ModelRouter : def __init__ ( self ): self . classifier = " qwen2.5-1.5b " self . specialists = { " code " : " qwen2.5-coder-7b " , " math " : " qwen2.5-32b " , " creative " : " claude-sonnet-4 " , " general " : " qwen2.5-7b " , } def route ( self , prompt : str ) -> str : task_type = self . classify ( prompt ) model = self . specialists . get ( task_type , self . specialists [ " general " ]) return self . call_m

Building a high-performance Polymarket trading bot requires mastering its unique hybrid architecture:...

pgrac is an open attempt to rebuild Oracle RAC's core machinery (shared-everything storage, multiple active nodes all writing one database, a cluster-wide change number) on top of PostgreSQL 16. Build log #1 laid out the four problems that fight back. This one is about the problem that turns a node failure into silent data corruption, and the first, deliberately modest, layer pgrac ships against it. The failure mode In a shared-nothing cluster an evicted node is mostly harmless: it owns its own disks, so the cluster routes around it. In a shared-everything cluster the same event is dangerous, because every node writes the same storage. Picture the classic split: node 2 misses heartbeats, the cluster declares it dead and remasters its work elsewhere, but node 2 is not actually dead. It is frozen on a long GC pause, or its interconnect NIC flaked, and it is about to wake up and finish the write it started. Now two nodes believe they own the same blocks, and shared storage will accept both writes. That is not a crash. It is corruption you find three days later. Oracle RAC's answer is I/O fencing: before remastering a dead node's resources, you make certain it can no longer touch the storage, with STONITH, SCSI-3 persistent reservations, or a hardware watchdog. The node is fenced at a layer below its own software, because the whole point is that you cannot trust the dead node's software to behave. That hardware layer is real work, and it is not what pgrac built first. What it built first is the layer above it: an in-process cooperative write-fence, now default-ON. The rest of this is precise about what that does and does not buy you, because "we have fencing" is the kind of claim that is worth less than nothing if it is overstated. A fence needs an authority everyone can agree on You cannot fence on local opinion, because the whole problem is that the dead node disagrees about being dead. Authority has to live on durable, shared, quorum-backed storage. pgrac writes a sm