Advanced Topics

Rolling updates, multi-arch, init systems, build from source.

Rolling Updates

SwarmCracker supports zero-downtime rolling updates via SwarmKit orchestration.

How It Works

Manager creates new task with updated spec
SwarmCracker starts new Firecracker VM
VM reports RUNNING status
Manager waits for Monitor period (default: 5s)
Manager stops old task
Executor removes old VM

Update a Service

# Update image (triggers rolling update)
swarmctl update svc-nginx --image nginx:1.25

# Update with environment
swarmctl update svc-app --env LOG_LEVEL=debug

Configuration

SwarmKit controls update behavior (not SwarmCracker):

Parameter	Default	Description
Parallelism	1	Tasks updated simultaneously
Delay	0s	Wait between batches
Monitor	5s	Verify task stability
Failure Action	pause	On failure: pause/continue/rollback

Multi-Architecture Support

SwarmCracker supports multiple CPU architectures via placement constraints.

Supported Architectures

Arch	Firecracker Support	Notes
x86_64	✅ Full support	Primary target
arm64	✅ Experimental	AWS Graviton, Ampere

Architecture Constraints

# Create service constrained to x86_64 nodes
swarmctl create-service nginx:latest --constraint arch==x86_64

# Create service constrained to arm64 nodes
swarmctl create-service arm-app:latest --constraint arch==arm64

Multi-Arch Images

Use OCI image indexes for cross-arch compatibility:

# Build multi-arch image
docker buildx build --platform linux/amd64,linux/arm64 -t myapp:latest .

# SwarmCracker pulls correct variant based on node arch

Init Systems

MicroVMs need an init system for proper process management.

Why Init Matters

Zombie reaping — Orphan processes must be reaped
Signal handling — Forward SIGTERM to children
Process supervision — Restart failed processes

Supported Init Systems

Init	Size	Features
tini	~20KB	Minimal, Docker default
dumb-init	~30KB	Signal proxy, lightweight
s6	~100KB	Process supervision
systemd	Large	Full service management

Configure Init

executor:
  init_system: tini        # none | tini | dumb-init
  init_grace_period: 10    # seconds before SIGKILL during shutdown

Rootfs with Init

# Install tini in rootfs
curl -fsSL https://github.com/krallin/tini/releases/download/v0.19.0/tini-static -o rootfs/sbin/tini
chmod +x rootfs/sbin/tini

Build from Source

Prerequisites

Go 1.26+
Git
Make

Clone and Build

# Clone repository
git clone https://github.com/restuhaqza/SwarmCracker
cd SwarmCracker

# Build binaries
make all

# Output:
# build/swarmcracker
# build/swarmd-firecracker
# build/swarmcracker-agent

# Install
sudo make install

Build Targets

make all           # Build all binaries
make swarmcracker  # Build the main CLI
make test          # Run unit tests
make lint          # Run linters
make fmt           # Format code
make clean         # Clean build artifacts
make install       # Install binaries to $GOPATH/bin

Development Build

# Build a debug/dev binary
go build -o build/swarmcracker ./cmd/swarmcracker

# Run the CLI
./build/swarmcracker --help

systemd Services

swarmcracker cluster init (manager) and swarmcracker cluster join (worker) generate and enable the systemd units for you:

swarmcracker-manager.service — runs swarmd-firecracker --manager on the manager
swarmcracker-worker.service — runs swarmd-firecracker on workers

Inspect and control them with systemd:

sudo systemctl status swarmcracker-manager
sudo systemctl restart swarmcracker-worker

# Logs
sudo journalctl -u swarmcracker-manager -f
sudo journalctl -u swarmcracker-worker -f

There is no standalone swarmcracker service.

File Management

Manage rootfs and kernel images.

Rootfs Directory

executor:
  rootfs_dir: "/var/lib/firecracker/rootfs"

Kernel Management

executor:
  kernel_path: "/usr/share/firecracker/vmlinux"

Image Storage

/var/lib/firecracker/
├── rootfs/                 # executor.rootfs_dir
│   ├── nginx-rootfs.ext4
│   └── redis-rootfs.ext4
└── golden/                 # prebuilt golden image artifacts

/usr/share/firecracker/
└── vmlinux                 # executor.kernel_path (default kernel)

Troubleshooting

Rolling Update Stuck

# Check task status
swarmctl ls-tasks

# Check node availability
swarmctl ls-nodes

# Force rollback if needed
swarmctl update <service-id> --image nginx:1.25-alpine

Init Process Missing

# Check init in rootfs
ls rootfs/sbin/tini

# Verify init binary
file rootfs/sbin/tini

Build Fails

# Check Go version
go version  # Must be 1.26+

# Check dependencies
go mod download

# Run lint for errors
make lint

See Also: Configuration | Contributing Guide