Sprint 289: Cross-Node Isolate Live Migration & Context Resumption 🌐
Welcome to Sprint 289 and 291! In modern cloud and edge architectures, applications must be elastically scalable. KnotenCore sets a new standard for virtual machine runtimes: we can halt running VM isolates mid-execution, serialize their full registers, transfer them across the network, and resume them on a remote cluster node with zero data or state loss.
📦 Serialization and Transport of the VMState
The key to live migration lies in the encapsulation of the virtual machine execution state (VMState). Rather than simply transferring static variables and code, we must package the active running state.
The serialized execution state in KnotenCore includes:
- Stack: The flat list containing active computation values.
- Frames: The call frames detailing return addresses and localized bindings.
- Instruction Pointer (IP): The precise program address of the next opcode to be executed.
- Globals & Heap: All variables bound to the isolate context.
- State Hash: The cryptographic checksum verifying state integrity.
🔄 Resumption Rectification & Work-Stealing (Sprint 291)
The initial Sprint 290 implementation contained a critical limitation: on receiving nodes, stack, frames, IP, and base pointers were discarded, causing execution to restart from IP = 0.
In Sprint 291, we patched this by adding the migration_state: Option field to VMIsolate. On spawn, the isolate checks for a migration payload, recovers the execution context, and continues running right where it left off.
Leveraging our lock-free cluster queues, nodes can dynamically pull (steal) payloads from overloaded nodes and run them locally, achieving optimal load balancing.
🧪 Robust Cluster Simulation
Our command-line tool utility knoten-init --cluster-sim verifies this migration lifecycle. It spawns simulated cluster nodes, halts a running VM isolate, migrates it, and asserts that the final math computation returns the correct result on the remote node. This proves that KnotenCore is ready for stateful edge networks.