Senior Software Engineer - Elasticsearch

9fin is a scaling start-up that powers global debt markets with its AI platform. We are looking for a Senior Software Engineer - Elasticsearch to join our team and work on maintaining and scaling the Elasticsearch cluster and its configuration. The role involves designing and tuning mappings, analyzers, and tokenizers for precise search relevance, optimizing query performance, and operating clusters in production.

Requirements

• 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.
• Deep understanding of Elasticsearch internals (inverted index, shards/replicas, segment merging, refresh/flush cycles) and how they impact performance and consistency.
• Strong experience designing and tuning mappings, analyzers, and tokenizers (custom analyzers, multi-fields, synonyms, stemming strategies) for precise search relevance
• Proven ability to optimize query performance (DSL queries, filters vs queries, aggregations, caching, profiling, avoiding expensive operations like script queries when possible)
• Hands-on experience operating clusters in production (index lifecycle management, shard allocation, scaling, monitoring, failure recovery, snapshot/restore)
• 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
• 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 experience delivering APIs, Service Oriented Architecture
• Strong working knowledge of SQL statements for retrieving data
• A good collaborator and communicator with cross functional engineering teammates and others within 9fin
• Code Quality: Through writing testable, maintainable code, and by engaging in code review for your own work and for reviewing others

Benefits

• Competitive Salary
• Equity options
• Pension
• Private Medical Insurance
• Paid sick leave with Income Protection for long periods of illness
• Group Life Assurance
• Season Ticket Loan & Cycle to Work schemes
• Time off
• 25 holiday days per year
• Local public holidays (with the ability to exchange them for alternative days)
• Hybrid working model
• Work abroad for up to 3 months a year
• 1 month paid sabbatical after 5 years of service
• Enhanced parental leave & flexible working arrangements available
• Professional learning and development budget
• Quarterly team socials
• Summer and Winter company social events