Multi Cloud Serverless Cold starts
Measuring cold starts on AWS, GCP and Azure with Prometheus
Published: Sunday, Nov 28, 2021 Last modified: Wednesday, Feb 19, 2025
Continuing from Serverless DX survey, there is now a new arm64 branch.
Since AWS claim arm64 (Graviton) is cheaper and faster than amd64, I was thinking how to test this objectively. My previous survey focused on DX, which is not objectively measurable!
I thought it might be fun to test managed runtime cold starts using my prometheus setup at home.
Measuring cold starts

blackbox.yml is the blackbox exporter configuration
http_cold:
prober: http
timeout: 5s
http:
preferred_ip_protocol: ip4
fail_if_body_not_matches_regexp:
- "<title>Count: 1</title>"
The http function I have running across the major clouds counts up when invoked. How do I know it’s a cold start?
The count is one when it’s a cold start!
My home Prometheus monitor is configured with my http function endpoints:
- job_name: sls
params:
module: [http_cold]
static_configs:
- targets:
- https://sam.dabase.com/
- https://sarm.dabase.com/
labels:
cloud: aws
- targets:
- https://asia-east2-idiotbox.cloudfunctions.net/Countpage
- https://count.dabase.com/
labels:
cloud: gcp
- targets:
- https://counttesting.azurewebsites.net/
labels:
cloud: azure
The query to plot the cold starts is:
probe_duration_seconds{job="sls"} and probe_success{job="sls"}
Unsuccessful probes are typically when the serverless endpoint is not cold, so we ignore those.
Preliminary results
Azure is unsurprisingly slow since it’s hosted in Hong Kong, and my BBE is in my home in Singapore.
Is arm64 faster than x86_64? … it would appear so!

But .. the fastest surprisingly is … Google Cloud Platform Cloud Run!

🤯