docker: Images >1.2GB due to missing .dockerignore and multi-stage build

[Cripto5588]

[BUG] Docker images >1.2GB due to missing .dockerignore and multi-stage builds

Current Problem

The dockerfiles/avail-node.Dockerfile builds images 1.24GB+, making deploys impractical:

Local benchmark:

docker build -f dockerfiles/avail-node.Dockerfile -t avail:current .
# => 1.24GB, 8 layers, 6min+ build time

Root causes:

• No .dockerignore: Copies entire repo (.git/, target/, benches/) → 800MB+ bloat
• No multi-stage: Full Rust toolchain (200+MB) leaks into runtime image
• Unoptimized layers: 8+ layers vs typical Substrate 3-4 layers

Impact:

• Slow CI/CD pipelines (6min+ builds)
• High GHCR/DockerHub storage costs
• Poor node operator DX (slow deploys)
• Larger attack surface (toolchain binaries)

Substrate Comparison

Production Substrate/Polkadot nodes: ~350-450MB. Avail is 3x larger than industry standard.

Expected behavior: Lean runtime images (<500MB) following Substrate best practices.

@avail-node-team - Confirming this needs attention?

[Cripto5588]

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Security Note: This is a performance optimization issue, not a security vulnerability. No credentials or secrets are exposed in the current build process.