Container metrics collection in Docker - Step-by-Step Execution

Process Flow - Container metrics collection

Start Container

↓

Enable Metrics Collection

↓

Collect Metrics Data

↓

Store Metrics in Database

↓

Query Metrics for Analysis

↓

Use Metrics for Monitoring/Alerting

This flow shows how container metrics are collected, stored, and used for monitoring.

Execution Sample

Docker

docker stats --no-stream --format "{{.Container}} {{.CPUPerc}} {{.MemUsage}}"
INSERT INTO container_metrics (container_id, cpu_percent, memory_usage) VALUES (?, ?, ?);
SELECT * FROM container_metrics WHERE container_id = ?;

This code collects live container metrics, stores them in a database, and queries them.

Process Table

Step	Action	Input/Command	Output/Result	Notes
1	Start container	docker run -d nginx	Container ID: abc123	Container abc123 is running
2	Collect metrics	docker stats --no-stream --format "{{.Container}} {{.CPUPerc}} {{.MemUsage}}"	abc123 0.05% 10MiB / 500MiB	Metrics snapshot taken
3	Insert metrics	INSERT INTO container_metrics VALUES ('abc123', 0.05, '10MiB / 500MiB')	1 row inserted	Metrics stored in DB
4	Query metrics	SELECT * FROM container_metrics WHERE container_id = 'abc123'	abc123 | 0.05 | 10MiB / 500MiB	Retrieved stored metrics
5	End	-	-	Process complete

💡 Metrics collected once; process ends after storing and querying metrics.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
container_id	null	abc123	abc123	abc123	abc123	abc123
cpu_percent	null	null	0.05	0.05	0.05	0.05
memory_usage	null	null	10MiB / 500MiB	10MiB / 500MiB	10MiB / 500MiB	10MiB / 500MiB

Key Moments - 3 Insights

Why do we use --no-stream with docker stats?

Using --no-stream makes docker stats output a single snapshot instead of continuous updates, as shown in step 2 of the execution_table.

Why do we store metrics in a database after collecting them?

Storing metrics allows querying and historical analysis later, demonstrated in steps 3 and 4 where metrics are inserted and then retrieved.

What does the memory usage value '10MiB / 500MiB' mean?

It shows current memory used (10MiB) out of total available (500MiB), as seen in step 2 output.

Visual Quiz - 3 Questions

Look at the execution_table, what is the container_id after step 1?

A null

B abc123

C nginx

D 0.05

💡 Hint

Check the 'Output/Result' column in row for step 1.

At which step is the metrics data inserted into the database?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look for the 'Insert metrics' action in the execution_table.

If we remove --no-stream from docker stats, what changes in the execution?

A Container would stop running

B Metrics would not be collected at all

C Metrics would be collected continuously, not just once

D Database insertion would fail

💡 Hint

Refer to the key_moments explanation about --no-stream option.

Concept Snapshot

Container metrics collection:
- Start container
- Use 'docker stats --no-stream' for one-time metrics
- Parse output (container ID, CPU %, memory)
- Store metrics in database
- Query metrics for monitoring or analysis

Full Transcript

This visual execution trace shows how container metrics are collected using docker commands, stored in a database, and queried for analysis. First, a container is started and identified by its container ID. Then, the 'docker stats' command with the --no-stream option collects a single snapshot of CPU and memory usage. These metrics are inserted into a database table for storage. Finally, the stored metrics can be queried to retrieve the data for monitoring or alerting purposes. Key points include using --no-stream to avoid continuous streaming and understanding the memory usage format. This process helps monitor container performance effectively.