Capybara: Dynamic Load Balancing with Microsecond-Scale TCP Migration

Source release and artifact-evaluation kit for the SIGCOMM 2026 paper. The evaluated snapshot is release sigcomm26-ae-v1.2. Capybara is an L4 load balancer that rebalances established TCP connections through microsecond-scale live connection migration, co-designed between a P4 programmable switch and a kernel-bypass host stack (built on Demikernel).

Layout

Path	Contents
src/	the Capybara host stack (Rust): TCP/IP stack, migration protocol, transport interface
p4/	Tofino switch programs (L4 load balancing, migration co-design, per-figure eval variants)
examples/	applications used in the evaluation (HTTP server, proxy, Redis shim glue)
eval/, scripts/	evaluation and data-processing scripts
config/	per-host configuration templates
AE/	the artifact-evaluation kit: per-figure runners, sample data, expected results, switch programs, source provenance (see below)

Building

The host stack builds with the standard Demikernel toolchain (Rust nightly per rust-toolchain, DPDK with the mlx5 PMD; see Makefile). The switch programs target Intel Tofino, Barefoot SDE 9.4.

Reproducing the paper's results

The evaluation requires a physical testbed: a Tofino switch (APS BF6064X-T) and six servers with Mellanox ConnectX-5 100 GbE NICs. It is not reproducible on virtual hardware. For SIGCOMM'26 artifact evaluation, reviewers receive SSH access to the authors' testbed, where a run kit maps each paper claim to a one-command runner; access instructions are provided through the AE submission. Anyone with equivalent hardware can adapt the switch programs and scripts in this release.

On the testbed, each figure is one command from ~/capybara-AE-runs/ (its README has the full expected tables and tolerances):

Claim (from the abstract)	Figure	Command	Time
Up to 149x lower p99 tail latency under skew	Fig 7	bash fig7/run_fig7.sh quick (or full)	~18 / 45 min
Continuous rebalancing vs reactive/static	Fig 8	bash fig8/run_fig8.sh	~6 min
Works for stateful Redis (POSIX shim)	Fig 9	bash fig9/run_fig9.sh	~6 min
>2x throughput at 12 servers under skew	Fig 10	bash fig10/run_fig10.sh quick (or full)	~40 / 80 min
Benefits L7 LB; Prism collapses open-loop	Fig 11	bash fig11/run_fig11.sh (or full)	~45 / 70 min
Migration <3 us CPU, <15 us e2e; TCP+TLS	Fig 14	bash fig14/run_fig14.sh	~9 min

Each runner brings up the switch program and host stacks it needs, runs the experiment, regenerates the figure with the paper's own plotting code from that run's data, and restores the cluster to a clean baseline.

The artifact-evaluation kit (AE/)

AE/ is the run kit exactly as deployed in the reviewer account on the testbed (~/capybara-AE-runs/), so what a reviewer runs can be read here first:

Path	Contents
AE/README.md	reviewer entry point: claims-to-commands table, expected numbers, pacing, cleanup
AE/ENVIRONMENT.md	the testbed hardware and software, in full
AE/WALKTHROUGH.pdf	one complete recorded pass: every command, its duration, console output, and figure
AE/figN/	one directory per figure: run_figN.sh, its helpers, a README with expected results, and the authors' reference measurements
AE/sample-data/, AE/sample-figures/	measurements from the authors' runs and the figures drawn from them
AE/plot_from_samples.sh, AE/paperplot/	redraw every figure from the sample data with the paper's own plotting code, no hardware needed (pip install -r AE/requirements.txt)
AE/check_cluster.sh	read-only preflight of the testbed state
AE/cleanup_all.sh, AE/arm_watchdog.sh	restore the cluster from any state; deadman timer
AE/switch/	the per-figure Tofino programs and control-plane scripts as they exist on the switch
AE/source/	which branch, commit, diff and binary produced each figure (SOURCE.md)
AE/patches/	client-side patches and configs for the load generator

The per-figure host-stack trees are the ae-fig7, ae-fig8, ae-fig9 and ae-fig10 branches of this repository; the load-generator trees are the ae-* branches of ihchoi12/caladan. AE/source/SOURCE.md has the full map.

Redraw the figures without hardware

pip install -r AE/requirements.txt      # pandas, numpy, matplotlib, brokenaxes
bash AE/plot_from_samples.sh            # all six -> AE/sample-figures/
bash AE/plot_from_samples.sh 7 10       # a subset

License

See LICENSE.txt (this release follows the licensing of the Demikernel codebase it builds on; see also NOTICE.md).