Sylvain J
Principal Software Engineer at Elastic
France
Summary
🤩
Rockstar🎓
Top SchoolSylvain J is a Principal Software Engineer based in France with 12+ years building robust Java-based systems and low-level JVM instrumentation for production observability and security. His career spans startups and large companies—shipping Java agents from inception to paying customers at Sqreen and contributing to prominent open-source projects like OpenTelemetry and Elastic APM where he worked on bytecode instrumentation and JPMS compatibility. He is comfortable across the full stack, from databases (Cassandra, MySQL) to front-end work, and favors simple, maintainable designs over trendy complexity. Known for deep attention to code quality and performance, he pairs practical tooling expertise (Git, Vim, Linux, shell) with hands-on profiling and optimization to keep runtime overhead minimal. An unusual strength is his long history of working directly with bytecode/agent internals (ASM/ByteBuddy) across many JDKs and app servers, making him a go-to engineer for hard-to-reproduce production problems.
12 years of coding experience
16 years of employment as a software developer
Diplôme d'Ingénieur Computer Science, Diplôme d'Ingénieur Computer Science at UTBMFrench DUT (Polytechnics) Computer Science, French DUT (Polytechnics) Computer Science at IUT Valence
English, French
Github Skills (13)
javas10
performance-monitor10
performance-monitoring10
bytebuddy10
application-monitoring10
bytecode10
java10
apm10
testing10
json-serialization9
error-handling9
opentelemetry9
sql6
Programming languages (13)
Github contributions (5)
elastic/apm-agent-java
Oct 2019 - Jan 2023
Role in this project:
Back-end Developer
Back-end DeveloperContributions:4 releases, 986 reviews, 296 commits in 3 years 4 months
Contributions summary:Sylvain primarily contributed to the Java agent for Elastic APM, focusing on implementing and improving core features related to error reporting, tracing, and configuration. This includes adding functionalities like capturing exception causes, implementing a mechanism to ignore specific exceptions, integrating support for multiple tracing headers, and enhancing database statement capture for SQL Server. The commits also cover improvements to JSON serialization tests, ensuring the correct representation of data in the APM backend.
agentapmelasticjava-agenttracing
open-telemetry/opentelemetry-java-instrumentation
Jun 2023 - Apr 2025
OpenTelemetry auto-instrumentation and instrumentation libraries for Java
Role in this project:Back-end Developer
Back-end DeveloperContributions:95 reviews, 35 PRs, 163 comments in 1 year 9 months
Contributions summary:Sylvain primarily focused on Java code and bytecode instrumentation within the OpenTelemetry Java instrumentation project. Their contributions involved upgrading bytecode versions for invokedynamic dispatch and ensuring compatibility with newer ByteBuddy versions. They also made improvements to testing and utilized Java-specific libraries, semconv attributes and also addressed module issues related to JPMS for improved project build and functionality.
instrumentationinstrumentation-librariesjava-agenttracingauto-instrumentation
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