> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Demo Resource Limits

> Learn to manage memory and CPU usage in Docker containers for predictable performance and host protection.

In this lesson, you’ll learn how to manage memory and CPU usage in Docker containers. Proper resource constraints help ensure predictable performance and protect the host from runaway containers.

## Table of Contents

* [Memory Limits](#memory-limits)
  * [Default Behavior](#default-behavior)
  * [Hard Memory Limit](#hard-memory-limit)
  * [Unlimited Swap](#unlimited-swap)
  * [Soft Memory Reservation](#soft-memory-reservation)
  * [Memory Flags Summary](#memory-flags-summary)
* [CPU Limits](#cpu-limits)
  * [Limiting CPU Count](#limiting-cpu-count)
  * [Pinning to Specific Cores](#pinning-to-specific-cores)
  * [CPU Flags Summary](#cpu-flags-summary)

***

## Memory Limits

Docker containers run without memory constraints by default. You can view and modify these settings using `docker run` flags.

### Default Behavior

Run a container named **testone** without any memory restrictions:

```bash theme={null}
docker container run -itd --name=testone ubuntu
```

Inspect its memory settings:

```bash theme={null}
docker container inspect testone | grep -i mem
```

Output:

```json theme={null}
"Memory": 0,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": null
```

A value of `0` indicates “no limit.”

### Hard Memory Limit

Set a hard cap on RAM usage with `--memory`. The following command limits the container to **200 MiB**:

```bash theme={null}
docker container run -itd --name=testtwo --memory=200m ubuntu
```

Verify:

```bash theme={null}
docker container inspect testtwo | grep -i mem
```

Expected:

```json theme={null}
"Memory": 209715200,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": null
```

### Unlimited Swap

By default, swap is limited to the same size as `--memory`. To allow unlimited swap, use `--memory-swap=-1`:

```bash theme={null}
docker container run -itd \
  --name=testthree \
  --memory=200m \
  --memory-swap=-1 \
  ubuntu
```

Inspect:

```bash theme={null}
docker container inspect testthree | grep -i mem
```

Result:

```json theme={null}
"Memory": 209715200,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 0,
"MemorySwap": -1,
"MemorySwappiness": null
```

<Callout icon="triangle-alert" color="#FF6B6B">
  Unlimited swap (`MemorySwap: -1`) can lead to performance degradation if the host starts swapping heavily. Monitor your containers closely when using this option.
</Callout>

### Soft Memory Reservation

With `--memory-reservation`, you set a **soft limit** that Docker tries to enforce under memory contention:

```bash theme={null}
docker container run -itd \
  --name=testfour \
  --memory=200m \
  --memory-reservation=100m \
  --memory-swap=-1 \
  ubuntu
```

Inspect:

```bash theme={null}
docker container inspect testfour | grep -i mem
```

Output:

```json theme={null}
"Memory": 209715200,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 104857600,
"MemorySwap": -1,
"MemorySwappiness": null
```

This configuration guarantees between **100 MiB** and **200 MiB** of RAM, with unlimited swap.

### Memory Flags Summary

| Flag                 | Description                                  | Example                     |
| -------------------- | -------------------------------------------- | --------------------------- |
| --memory             | Hard limit for container memory              | `--memory=200m`             |
| --memory-reservation | Soft (guaranteed) memory reservation         | `--memory-reservation=100m` |
| --memory-swap        | Total memory + swap limit (`-1` = unlimited) | `--memory-swap=-1`          |
| --memory-swappiness  | Tendency to swap (0–100)                     | `--memory-swappiness=10`    |

***

## CPU Limits

Docker lets you restrict CPU usage by setting the number of CPUs or pinning containers to specific cores.

### Limiting CPU Count

First, check your host’s CPU count:

```bash theme={null}
nproc
```

Assuming **2** cores, limit the container to **1** CPU:

```bash theme={null}
docker container run -itd --name=testcpu --cpus=1 ubuntu
```

Inspect:

```bash theme={null}
docker container inspect testcpu | grep -i nano
```

You’ll see:

```json theme={null}
"NanoCpus": 1000000000,
```

`NanoCpus: 1000000000` represents 1 full CPU core.

### Pinning to Specific Cores

Use `--cpuset-cpus` to bind a container to specific cores. For example, pin to core **1**:

```bash theme={null}
docker container run -itd --name=testcpus --cpuset-cpus="1" ubuntu
```

Inspect:

```bash theme={null}
docker container inspect testcpus | grep -i cpuset
```

Output:

```json theme={null}
"CpusetCpus": "1",
```

This container will only run on CPU core 1.

### CPU Flags Summary

| Flag          | Description                         | Example               |
| ------------- | ----------------------------------- | --------------------- |
| --cpus        | Number of CPU cores (fractional OK) | `--cpus=1.5`          |
| --cpuset-cpus | Bind container to specific cores    | `--cpuset-cpus="0,1"` |

***

## Links and References

* [Docker Run Reference](https://docs.docker.com/engine/reference/run/)
* [Docker Resource Management](https://docs.docker.com/config/containers/resource_constraints/)
* [Kubernetes Limits and Requests](https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/)

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