River - Senior Software Engineer
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:date: 2025-11-06

To River:

Over 15 years building & scaling systems, with deep experience in financial infrastructure & cryptographic implementations, positions me well for the Senior Software Engineer role at River. At Cofense (2020-2022), implemented Terraform-based AWS account controls & compliance automation for SOC2 & FedRAMP environments, managing security at scale. At Remind (2017-2020), managed infrastructure for 60+ microservices supporting 30 million users, ensuring critical services scaled during COVID-19 lockdowns. At Coursemojo (2022-2025), designed CI/CD pipelines, scaled AI-powered educational tools, & implemented real-time websocket features. Founded & bootstrapped Make Post Sell (2019), building commission-free e-commerce with open-sourced hot wallet payments for Dogecoin & Monero. The payment system generates temporary single-use addresses per order, sweeps funds to shop owner cold wallets in self-custody, & implements an automated quote state machine that handles overpayments/underpayments with automatic refunds, zero human intervention. This production crypto payment architecture, combined with experience scaling systems at 30M+ user scale, aligns directly with River's mission to build reliable Bitcoin financial infrastructure.

I've been working with Elixir on hobby & bootstrapped projects, including GumYum NPC API (game character interaction service) & lxc-code-executor (secure code execution in LXC containers). While Python is my primary production stack (Flask, Pyramid, SQLAlchemy), I've grown to appreciate Elixir's concurrency model, pattern matching, & fault tolerance, making it ideal for building reliable financial systems. Building hot wallet integrations for Dogecoin & Monero taught me the challenges of handling real crypto transactions: managing private keys securely, verifying blockchain confirmations, handling network forks, & designing systems that never lose track of money. The chance to work with a team building a Bitcoin-focused financial institution, backed by investors like Polychain & focused on self-custody & transparency, represents exactly the kind of mission-driven work I'm seeking. I'd love to apply my full-stack engineering experience, Elixir knowledge, security mindset, & hands-on cryptocurrency implementation experience to help River scale & deliver value to Bitcoin users.

Russell Ballestrini
