Question: I am running command `docker stats <container_id> > performance.txt` over a period of 1 hour during multi-user testing. Some stats like memory, CPU increase, then normalize. But, it is with NET I/O value that it kept on increasing.

At the start, the O/P was:

```
NAME                CPU %               MEM USAGE / LIMIT    NET I/O             BLOCK I/O           PIDS
my-service            0.10%               5.63GiB / 503.6GiB   310MB / 190MB       0B / 0B             80
NAME                CPU %               MEM USAGE / LIMIT    NET I/O             BLOCK I/O           PIDS
my-service            0.20%               5.63GiB / 503.6GiB   310MB / 190MB       0B / 0B             80

```

After 1 hour, it is:

```
NAME                CPU %               MEM USAGE / LIMIT     NET I/O             BLOCK I/O           PIDS
my-service            116.26%             11.54GiB / 503.6GiB   891MB / 523MB       0B / 0B             89
NAME                CPU %               MEM USAGE / LIMIT     NET I/O             BLOCK I/O           PIDS
my-service            8.52%               11.54GiB / 503.6GiB   892MB / 523MB       0B / 0B             89

```

As above, the value of NET I/O is always increasing. What can it probably mean?
Docker documentation says it is the input received and output given by the container. If so, then why is it increasing? Is there some issue with the image running in the container?

Answer: 
`NET I/O` is a cumulative counter. It only goes up (when your app receives and sends data).

<https://docs.docker.com/engine/reference/commandline/stats/>

> 
> 
> 
> 
> | Column name | Description |
> | --- | --- |
> | NET I/O | The amount of data the container has sent and received over its network interface |
> 
> 
> 

So it's accumulated over time. Unlike, say, `CPU %` which is how much CPU the container is using *right now*.
> 
> The docker stats command returns a live **data stream** for **running containers**.
> 
> 
> 

It's considered the total amount of data passed over the network since the container started. From the definition of stream:

> 
> computing
> a continuous flow of data or instructions,
> 
> 
> 

It doesn't say that explicitly but you can obviously infer this by the term continuous or stream. Perhaps the documentation could be made a bit more clear in that respect.