Some embodiments of the invention provide a novel architecture for providing context-aware middlebox services at the edge of a physical datacenter. In some embodiments, the middlebox service engines run in an edge host (e.g., an NSX Edge) that provides routing services and connectivity to external networks (e.g., networks external to an NSX-T deployment). Some embodiments use a novel architecture for capturing contextual attributes on host computers that execute one or more machines and providing the captured contextual attributes to context-aware middlebox service engines providing the context-aware middlebox services. In some embodiments, a context header insertion processor uses contextual attributes to generate a header including data regarding the contextual attributes (a “context header”) that is used to encapsulate a data message that is processed by the SFE and sent to the context-aware middlebox service engine.