Senior Software Engineer - Elasticsearch

Responsibilities

• As part of the retrieval team, you will be one of the core maintainers of the Elasticsearch cluster and its configuration.
• You'll work closely with a senior team of both backend, AI and Data engineers to own and scale the search infrastructure at 9fin.
• Exposure to the development and engineering on the backend services and web application hosted tools and systems of the 9fin platform.
• Play an impactful role as a senior IC, running code reviews, mentoring other developers, leadership & involvement in early research and experimentation with new technologies providing input for new features and products.
• Continually improve the 9fin codebase taking the chance to automate, refactor and document when it's most impactful.
• Very diverse web platforms, from complex financial data modelling, complex access control business logic, capturing environmental, emission, energy data, incorporation of ML/AI prediction services, data visualisation serving and automation systems.
• Developer Experience: Through managed automated preview environments, feature flags and well maintained non production environments. You will be able to move with velocity and get feedback and iterate quickly.
• Our Backend Stack
• Python is the dominant backend language used
• Flask & FastAPI
• Typing is used within our Python stack to power automated documentation and API definitions
• Relational Databases (PostgreSQL) at the heart of majority of services
• We have our own internal developer platform with standardised paved road approaches to infrastructure to bring your code into production as quickly as possible.
• We're AWS for Cloud hosted services
• Heavy use of AWS lambda Serverless
• Docker (AWS ECS) for uniform development/deployment from dev to prod
• Elastic Search deployment hosted in Elastic Cloud

Requirements

• This role will be a great fit if you:
• Have experience operating as a Senior IC Engineer, leading systems design and infrastructure discussions, mentoring more junior team members, and scoping work within cross-functional product teams.
• Have a deep understanding of Elasticsearch internals (inverted index, shards/replicas, segment merging, refresh/flush cycles) and how they impact performance and consistency.
• Have strong experience designing and tuning mappings, analyzers, and tokenizers (custom analyzers, multi-fields, synonyms, stemming strategies) for precise search relevance
• Have proven ability to optimize query performance (DSL queries, filters vs queries, aggregations, caching, profiling, avoiding expensive operations like script queries when possible)
• Have a hands-on experience operating clusters in production (index lifecycle management, shard allocation, scaling, monitoring, failure recovery, snapshot/restore)
• Have a solid knowledge of distributed systems concepts (consistency, partitioning, replication, eventual consistency) and how Elasticsearch behaves under load and failure scenarios.
• Plan and reason about software effectively, clearly and compellingly communicating its purpose within systems and its business impact on clients
• Have hands-on experience designing data flow through software, from persistent storage to API endpoints, while applying industry best practices for validation
• Experience with Python and its web frameworks (we currently use FastAPI with strong typing & Pydantic)
• Strong exper

Benefits

Additional Information

About 9fin 9fin is the AI platform powering global debt markets - the world's largest asset class at over $145 trillion. Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets. Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption. We're at a defining inflection point. With proven product-market fit and strong, global market pull, 9fin is accelerating toward becoming the category-defining platform for debt markets worldwide.

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