What is Docker Stats? | DevOps Dictionary

Docker Stats — Real-Time Container Resource Monitoring

What Is Docker Stats in Simple Terms?

docker stats is the quickest way to see what resources your containers are consuming right now — CPU usage, memory usage, network traffic, and disk I/O, updated every second in your terminal.

Bash

# Live stats for all running containers
docker stats
 
# Output:
# CONTAINER    CPU %   MEM USAGE/LIMIT    MEM %   NET I/O      BLOCK I/O
# payment-api  2.5%    128MiB/512MiB      25.0%   2MB/1MB      0B/0B
# postgres     0.8%    256MiB/1GiB        25.0%   100B/50B     50MB/5MB
# redis        0.1%    12MiB/512MiB       2.3%    500B/200B    1MB/0B

Reading the Output

◈ DIAGRAM

CONTAINER    <- container name or ID
CPU %        <- CPU usage as % of total host CPU
               (200% = 2 full cores on a 4-core host)
MEM USAGE    <- current memory used
MEM LIMIT    <- memory limit set for container
MEM %        <- (MEM USAGE / MEM LIMIT) * 100
               Warning: > 85% = approaching OOMKill
NET I/O      <- bytes received / transmitted over network
BLOCK I/O    <- bytes read / written to disk
PIDs         <- number of processes inside container

Useful docker stats Patterns

Bash

# One-shot snapshot (no live update) — for scripts and CI
docker stats --no-stream
 
# Stats for specific containers only
docker stats payment-api postgres
 
# Formatted output for scripting
docker stats --no-stream \
  --format "{{.Name}}: CPU={{.CPUPerc}} MEM={{.MemUsage}} ({{.MemPerc}})"
# payment-api: CPU=2.5% MEM=128MiB / 512MiB (25.0%)
# postgres: CPU=0.8% MEM=256MiB / 1GiB (25.0%)
 
# Watch for memory pressure — alert if any container above 85%
docker stats --no-stream --format \
  '{{.Name}} {{.MemPerc}}' | \
  awk '{gsub("%","",$2); if($2>85) print "WARNING: " $1 " at " $2 "%"}'
 
# Continuous monitoring with timestamps
watch -n 5 'docker stats --no-stream'

Updating Limits on Running Containers

Bash

# If stats shows a container approaching its memory limit:
docker update --memory 1g payment-api
docker update --cpus 2 payment-api
# Changes cgroup limits live — no restart needed
# Useful for emergency capacity increase during incidents

Docker Stats vs Prometheus

Bash

docker stats:
  Good for: quick checks, development, debugging
  Bad for: alerting, historical data, multi-host
  No persistence, terminal-only
 
Prometheus + cAdvisor:
  Good for: production monitoring, alerting, dashboards
  Collects same metrics as docker stats but persistently
  Works across multiple hosts
  Use for production

PLACEMENT PRO TIP
**Tip:** Memory percentage (`MEM %`) is the most important column to watch. When a container reaches 100% of its memory limit, the kernel kills it immediately (OOMKill, exit code 137). Set alerts when any container exceeds 85% — that gives you time to investigate and increase the limit before the OOMKill happens.