3.1 The docker stats Command
Docker gives you a handy built-in tool for real-time container monitoring — the docker stats command. This command lets you track key performance metrics for your containers, like CPU, memory, network, and disk usage. Let’s dive into how to use docker stats to get insights into your containers' status and performance.
The docker stats command provides dynamic stats on container performance in real time. It shows the following metrics for each container:
- CPU %: the percentage of CPU usage by the container.
- MEM USAGE / LIMIT: the memory usage by the container and its set limit.
- MEM %: the percentage of memory usage by the container.
- NET I/O: network traffic (incoming and outgoing).
- BLOCK I/O: the amount of disk input/output operations.
- PIDS: the number of processes running inside the container.
Basic Usage of the docker stats Command
Running the docker stats command without parameters displays metrics for all running containers:
docker stats
Example output for the docker stats command:
CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
d9b100f2f636 my_nginx 0.07% 1.24MiB / 1.952GiB 0.06% 1.68kB / 0B 0B / 12.3MB 2
fa3f3f3f3f3f my_postgres 2.13% 230.5MiB / 1.952GiB 11.52% 2.12MB / 2.05MB 85.6MB / 45.2MB 10
Monitoring a Specific Container
You can track metrics for a specific container by specifying its name or ID:
docker stats my_nginx
3.2 Settings for the docker stats Command
Options for the docker stats Command
The docker stats command supports several options to customize the output:
--allor-a: display metrics for all containers, including stopped ones.--no-stream: display metrics once and then exit the command.--format: customize output using templates.
Example of Using the --no-stream Option
Displaying metrics once for all containers:
docker stats --no-stream
Example of Using the --format Option
Formatted output:
docker stats --format "table {{.Container}}\t{{.CPUPerc}}\t{{.MemUsage}}"
Example of output:
CONTAINER ID CPU % MEM USAGE / LIMIT
d9b100f2f636 0.07% 1.24MiB / 1.952GiB
fa3f3f3f3f3f 2.13% 230.5MiB / 1.952GiB
3.3 Practical Use of docker stats
Example 1: Tracking Server Load
You can use docker stats to monitor containers on the server and identify containers with high CPU or memory usage. This helps you optimize resource usage and improve app performance.
docker stats
Example 2: Monitoring a Specific Container During Testing
When testing new app versions or changing configurations, you can monitor specific container metrics to ensure there's no negative impact on performance.
docker stats my_test_container
Example 3: Integration with Monitoring Systems
You can integrate the output of docker stats with external monitoring systems using the --format option to create an output format compatible with your monitoring tool.
docker stats --no-stream --format "{{.Container}}: CPU {{.CPUPerc}}, MEM {{.MemUsage}}"
Limitations of the docker stats Command
Although docker stats provides useful real-time metrics, it has some limitations:
- Limited Metrics: The command only displays basic metrics and doesn't provide detailed container state information.
- Manual Usage: docker stats is convenient for manual use, but for automated monitoring and alerting, it's better to use specialized tools like Prometheus and Grafana.
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