Rajan Kalwar
Senior Software Engineer · Cloud, Backend & GenAI Systems
Professional summary
Senior software engineer focused on AWS architecture, distributed backends, and production GenAI. I design secure APIs, event-driven workflows, container platforms, data models, and LLM applications—with explicit attention to deployment, permissions, failure behavior, and operational trade-offs.
Technical skills
- Languages
- Python, TypeScript, JavaScript
- Backend
- FastAPI, Flask, NestJS, Fastify, REST, GraphQL, Server-Sent Events
- AWS
- Lambda, ECS, Fargate, EC2, App Runner, ECR, API Gateway, AppSync, Cognito, VPC, IAM, S3, CloudFront, RDS
- Data and messaging
- DynamoDB, PostgreSQL, Redis, MongoDB, ArangoDB, SQS, SNS, EventBridge, Step Functions, DynamoDB Streams
- GenAI
- LangChain, LangGraph, LlamaIndex, RAG, vector retrieval, document ingestion, tool calling, response streaming, OpenAI-compatible APIs
- Infrastructure and delivery
- CloudFormation, Serverless Framework, Docker, CI/CD, private networking, least-privilege IAM, dead-letter queues, retry and failure handling
- GCP
- App Engine, Cloud Run, Firebase, Firestore, Functions, Pub/Sub
| Area | Technologies and practices |
|---|---|
| Languages | Python, TypeScript, JavaScript |
| Backend | FastAPI, Flask, NestJS, Fastify, REST, GraphQL, Server-Sent Events |
| AWS | Lambda, ECS, Fargate, EC2, App Runner, ECR, API Gateway, AppSync, Cognito, VPC, IAM, S3, CloudFront, RDS |
| Data and messaging | DynamoDB, PostgreSQL, Redis, MongoDB, ArangoDB, SQS, SNS, EventBridge, Step Functions, DynamoDB Streams |
| GenAI | LangChain, LangGraph, LlamaIndex, RAG, vector retrieval, document ingestion, tool calling, response streaming, OpenAI-compatible APIs |
| Infrastructure and delivery | CloudFormation, Serverless Framework, Docker, CI/CD, private networking, least-privilege IAM, dead-letter queues, retry and failure handling |
| GCP | App Engine, Cloud Run, Firebase, Firestore, Functions, Pub/Sub |
Experience
we45
Software Engineer
Cloud security training provider and hands-on learning platform.
- Develop, troubleshoot and maintain Backend supporting the learning platform, resolving platform issues and improving the stability of the overall services.
- Maintain the cloud infrastructure and backend systems supporting the company's security learning platform, ensuring reliability, availability, and smooth delivery of hands-on cloud security sandbox environments.
- Provision and configure AWS resources to reproduce real-world customer infrastructure, supporting cloud security assessments, attack-surface analysis, and security hardening validation.
- Collaborate with cloud security engineers to translate infrastructure requirements into reproducible AWS environments for testing security controls, misconfigurations, exposure paths, and potential attack vectors.
ShopSwap Inc.
Senior Software Engineer
Early-stage brand collaboration platform for cross-promotion and referral tracking.
- Designed and deployed cost-efficient serverless architectures on AWS using Lambda, DynamoDB, Cognito, API Gateway, and CloudFormation.
- Built and operated containerized workloads on AWS ECS with private VPC networking, ECR, and least-privilege IAM permissions.
- Designed scalable SQL and NoSQL data models using PostgreSQL and DynamoDB for high-performance application workloads.
- Developed distributed microservices using NestJS, Redis, and AWS App Runner.
- Built secure and scalable LLM-powered applications and RAG pipelines using LangChain, LangGraph, and LlamaIndex, with a focus on efficient token usage and reliable response generation.
Preparie Inc.
Software Engineer
Marketplace for home-cooked food ordering and delivery.
- Designed and developed GraphQL APIs using AWS AppSync, Lambda, and DynamoDB.
- Built high-throughput DynamoDB workloads using single-table design, optimized access patterns, and scalable data modeling.
- Designed and maintained AWS infrastructure supporting frontend and backend application workloads.
- Provisioned and managed cloud resources for reliable and scalable application delivery.
Bottle Tech
Cloud Engineer
Nepal-based technology company building in the IoT space.
- Built managed API-as-a-Service solutions using AWS API Gateway, including API keys, usage plans, throttling, and rate limiting.
- Contributed to the design and implementation of AWS infrastructure across multiple projects.
- Provisioned and maintained cloud resources supporting REST and GraphQL APIs.
- Built and maintained CI/CD pipelines, automated deployments, and managed infrastructure as code using AWS CloudFormation.
Selected engineering projects
ClientAPI Gateway REST APILambdaDynamoDB
API access management and usage controls
Designed and implemented an AWS-native control plane for issuing API keys and applying tier-specific throttles and quotas without building a custom rate limiter.
Engineering decisions
- Separated administrative key and plan operations from API-key-protected workloads.
- Returned raw key values only at creation; DynamoDB stores lifecycle metadata using a single-table model and entity-type index.
- Documented propagation delays, non-transactional edge cases, and cleanup behavior as explicit operating constraints.
HTTP APILambdaSQSLambdaSNSConsumers
Failure-aware asynchronous fan-out
Built a deployable event pipeline that buffers HTTP requests, processes them asynchronously, and fans out notification and audit events to independently operated consumers.
Engineering decisions
- Kept the queue visibility timeout above the processor timeout and isolated exhausted messages in a dead-letter queue after three failed receives.
- Used partial batch failure reporting so successful records are not processed again when another record fails.
- Scoped every IAM grant to the exact queue or topic it needs, rather than granting broad messaging access.
InternetALBPrivate subnetsECS service
Private container services on AWS
Created parallel Fargate and EC2-backed ECS implementations to compare capacity models while preserving the same private networking, load-balancing, and image-delivery boundaries.
Engineering decisions
- Kept tasks and container instances in private subnets behind a public Application Load Balancer.
- Split networking, capacity, image, and service resources by operational concern and staged deployment so ECR existed before service rollout.
- Configured the EC2 implementation with an Auto Scaling group and ECS capacity provider for a direct comparison with Fargate-managed capacity.
Additional public engineering work
- Streaming LLM responses from Lambda — Token-by-token delivery with Lambda Web Adapter, Flask, and Server-Sent Events.
- AppSync GraphQL authorization patterns — API-key, IAM, Cognito, and field-level authorization examples.
- EventBridge routing and decoupled consumers — Domain-event routing with independently subscribed consumers.
- Multi-AZ VPC and private DNS — Public/private subnet architecture with NAT, bastion access, and Route 53 private DNS.