What happened?
We wanted our vault-rebalancing logic to live entirely on-chain, using Chainlink's CCIP to send allocation instructions across multiple chains (Ethereum Sepolia, Base Sepolia, Arbitrum Sepolia, and Avalanche Fuji).

The hurdle

• CCIP message payloads needed to be optimized for efficient cross-chain communication while maintaining data integrity.
• Our allocation struct (

  PortfolioLib.Allocation

  ) contained multiple fields that needed proper serialization for CCIP transmission.
• Testnet relayer timeouts and message delivery verification required robust error handling and logging mechanisms.

How we overcame it

1. Optimized payload structure: Used a minimal

   abi.encode(strategyIndex, allocationAmount)

   format for CCIP messages, keeping only essential data (strategy index and amount) to minimize payload size while maintaining functionality.
2. Efficient struct design: Designed the

   PortfolioLib.Allocation

   struct with compact data types (

   uint64

   for chain selector,

   uint16

   for strategy index and percentage) to optimize gas usage and message size.
3. Enhanced CCIP integration: Implemented a dedicated

   CCIPRouterAdapter

   wrapper that handles message construction, fee calculation, and proper CCIP Router interaction with comprehensive error handling.
4. Comprehensive testing: Built extensive test suites including

   MockCCIPAdapter

   for local testing, cross-chain integration tests, and end-to-end scenarios to ensure reliable message delivery and proper strategy execution.

Result: our on-chain allocator now reliably bridges user funds to the highest-yield vault across any networks, fully automated via CCIP with optimized message payloads and robust error handling.