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Lambda MicroVM sample apps — image size comparison

Measured 2026-04-24 via ./measure-image-size.sh against linux/arm64 builds (native on Apple Silicon). Rebuild this file by running that script against each sample directory and pasting the output into the headline table below.

Headline numbers

App .Size (compressed, on-disk) Uncompressed rootfs (snapshot proxy) Ratio
sample-flask-app (bare, no observability) 51,432,099 B · 50 MiB 184,143,290 B · 176 MiB 3.6×
sample-flask-app-using-serverless-comp-poc 131,071,500 B · 125 MiB 535,250,990 B · 511 MiB 4.1×
sample-flask-app-serverless-init-poc 143,443,748 B · 137 MiB 575,000,990 B · 549 MiB 4.0×
sample-flask-app-datadog-agent-poc (full agent) 357,134,776 B · 341 MiB 1,256,124,490 B · 1.20 GiB 3.5×

Delta vs. bare Flask baseline

Cost of adding each observability layer on top of the minimal Flask app:

Variant Δ compressed Δ uncompressed
serverless-comp (PID-1 binary) +75 MiB +335 MiB
serverless-init (PID-1 binary) +87 MiB +373 MiB
full datadog-agent +291 MiB +1.03 GiB

Compressed-vs-uncompressed interpretation

Two numbers reflect two different questions:

  • Compressed (docker image inspect .Size): the Docker daemon's on-disk storage footprint. Closer to what's transferred over the network when an image is pulled.
  • Uncompressed: the summed layer additions from docker history. Closer to what the Firecracker snapshot will serialize — because the snapshot captures the extracted running filesystem plus guest memory, not the compressed blob.

For answering "how big will my MicroVM snapshot be, and how long will it take to clone?", the uncompressed column is the better proxy. The 3.5–4.1× compression ratio is consistent across all four, which matches the content mix (Python bytecode, Debian/AL2023 binaries, shared libraries — all moderately compressible).

Key takeaways

  1. The two serverless variants are within noise of each other. serverless-init and serverless-comp sit at 125–137 MiB compressed / 511–549 MiB uncompressed. They trade off on capability (serverless-init has richer lifecycle hooks; serverless-comp is purpose-built for init-mode with stdout capture), not on image weight.

  2. The full-agent variant is roughly 2.5× either serverless variant. On uncompressed footprint, the DD-agent POC (1.20 GiB) is ~2.2× serverless-init (549 MiB). The extra bulk is dominated by the datadog-agent RPM (~827 MB uncompressed by itself), which ships checks, autodiscovery, Python/Go runtimes, and sub-agents that the serverless-* variants deliberately strip.

  3. A minimal Flask app is ~3× smaller than the lightest observability variant. 50 MiB compressed baseline grows to 125 MiB (serverless-comp) — a 75 MiB tax to get APM/logs/lifecycle hooks. Reasonable for what you get.

  4. Clone latency implications. MicroVM snapshot clone time scales roughly with snapshot size. A 1.20 GiB snapshot for the full-agent POC will clone noticeably slower than a 176 MiB bare app, with the serverless variants sitting in between. Exact numbers depend on the MicroVM platform's backing storage, but the ordering is stable.

Platform observations

  • The sample-flask-app-using-serverless-comp-poc image was built 2026-04-16 (it's been in the buildx cache for ~1 week). The 125 MiB / 511 MiB numbers reflect whatever datadog-serverless-compat binary version was pinned at that build time.
  • All four images are ARM64-native; measurements on Apple Silicon are close to server-side Firecracker snapshot sizes (minus kernel/initramfs that the MicroVM layer adds post-build).
  • The server-side snapshotSizeBytes API field that would normally give the authoritative per-image snapshot size is not currently populated by the preview service. See PREVIEW-CAVEATS.md for the tracked gap; the uncompressed numbers above are the closest local proxy until the service catches up.

Reproducing this comparison

for dir in sample-flask-app \
           sample-flask-app-using-serverless-comp-poc \
           sample-flask-app-serverless-init-poc \
           sample-flask-app-datadog-agent-poc; do
  ./measure-image-size.sh "$dir"
done

Each invocation auto-removes the built image on exit (see the cleanup trap in measure-image-size.sh), so running all four in sequence leaves zero residue in the local Docker daemon.

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