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343 lines
7.3 KiB
Markdown
343 lines
7.3 KiB
Markdown
# Our sample application
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- Visit the GitHub repository with all the materials of this workshop:
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<br/>https://github.com/jpetazzo/container.training
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- The application is in the [dockercoins](
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https://github.com/jpetazzo/container.training/tree/master/dockercoins)
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subdirectory
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- Let's look at the general layout of the source code:
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there is a Compose file [docker-compose.yml](
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https://github.com/jpetazzo/container.training/blob/master/dockercoins/docker-compose.yml) ...
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... and 4 other services, each in its own directory:
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- `rng` = web service generating random bytes
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- `hasher` = web service computing hash of POSTed data
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- `worker` = background process using `rng` and `hasher`
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- `webui` = web interface to watch progress
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---
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class: extra-details
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## Compose file format version
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*Particularly relevant if you have used Compose before...*
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- Compose 1.6 introduced support for a new Compose file format (aka "v2")
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- Services are no longer at the top level, but under a `services` section
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- There has to be a `version` key at the top level, with value `"2"` (as a string, not an integer)
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- Containers are placed on a dedicated network, making links unnecessary
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- There are other minor differences, but upgrade is easy and straightforward
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---
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## Links, naming, and service discovery
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- Containers can have network aliases (resolvable through DNS)
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- Compose file version 2+ makes each container reachable through its service name
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- Compose file version 1 did require "links" sections
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- Our code can connect to services using their short name
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(instead of e.g. IP address or FQDN)
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- Network aliases are automatically namespaced
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(i.e. you can have multiple apps declaring and using a service named `database`)
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---
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## Example in `worker/worker.py`
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```python
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redis = Redis("`redis`")
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def get_random_bytes():
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r = requests.get("http://`rng`/32")
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return r.content
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def hash_bytes(data):
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r = requests.post("http://`hasher`/",
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data=data,
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headers={"Content-Type": "application/octet-stream"})
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```
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(Full source code available [here](
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https://github.com/jpetazzo/container.training/blob/8279a3bce9398f7c1a53bdd95187c53eda4e6435/dockercoins/worker/worker.py#L17
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))
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---
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## What's this application?
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--
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- It is a DockerCoin miner! .emoji[💰🐳📦🚢]
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--
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- No, you can't buy coffee with DockerCoins
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--
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- How DockerCoins works:
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- `worker` asks to `rng` to generate a few random bytes
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- `worker` feeds these bytes into `hasher`
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- and repeat forever!
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- every second, `worker` updates `redis` to indicate how many loops were done
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- `webui` queries `redis`, and computes and exposes "hashing speed" in your browser
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---
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## Getting the application source code
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- We will clone the GitHub repository
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- The repository also contains scripts and tools that we will use through the workshop
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.exercise[
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<!--
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```bash
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if [ -d container.training ]; then
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mv container.training container.training.$$
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fi
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```
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-->
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- Clone the repository on `node1`:
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```bash
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git clone git://github.com/jpetazzo/container.training
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```
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]
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(You can also fork the repository on GitHub and clone your fork if you prefer that.)
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---
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# Running the application
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Without further ado, let's start our application.
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.exercise[
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- Go to the `dockercoins` directory, in the cloned repo:
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```bash
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cd ~/container.training/dockercoins
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```
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- Use Compose to build and run all containers:
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```bash
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docker-compose up
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```
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<!--
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```longwait units of work done```
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```keys ^C```
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-->
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]
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Compose tells Docker to build all container images (pulling
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the corresponding base images), then starts all containers,
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and displays aggregated logs.
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---
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## Lots of logs
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- The application continuously generates logs
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- We can see the `worker` service making requests to `rng` and `hasher`
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- Let's put that in the background
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.exercise[
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- Stop the application by hitting `^C`
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]
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- `^C` stops all containers by sending them the `TERM` signal
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- Some containers exit immediately, others take longer
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<br/>(because they don't handle `SIGTERM` and end up being killed after a 10s timeout)
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---
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## Restarting in the background
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- Many flags and commands of Compose are modeled after those of `docker`
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.exercise[
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- Start the app in the background with the `-d` option:
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```bash
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docker-compose up -d
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```
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- Check that our app is running with the `ps` command:
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```bash
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docker-compose ps
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```
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]
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`docker-compose ps` also shows the ports exposed by the application.
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---
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class: extra-details
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## Viewing logs
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- The `docker-compose logs` command works like `docker logs`
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.exercise[
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- View all logs since container creation and exit when done:
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```bash
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docker-compose logs
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```
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- Stream container logs, starting at the last 10 lines for each container:
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```bash
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docker-compose logs --tail 10 --follow
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```
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<!--
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```wait units of work done```
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```keys ^C```
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-->
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]
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Tip: use `^S` and `^Q` to pause/resume log output.
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---
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class: extra-details
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## Upgrading from Compose 1.6
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.warning[The `logs` command has changed between Compose 1.6 and 1.7!]
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- Up to 1.6
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- `docker-compose logs` is the equivalent of `logs --follow`
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- `docker-compose logs` must be restarted if containers are added
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- Since 1.7
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- `--follow` must be specified explicitly
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- new containers are automatically picked up by `docker-compose logs`
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---
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## Connecting to the web UI
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- The `webui` container exposes a web dashboard; let's view it
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.exercise[
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- With a web browser, connect to `node1` on port 8000
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- Remember: the `nodeX` aliases are valid only on the nodes themselves
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- In your browser, you need to enter the IP address of your node
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<!-- ```open http://node1:8000``` -->
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]
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A drawing area should show up, and after a few seconds, a blue
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graph will appear.
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---
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class: self-paced, extra-details
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## If the graph doesn't load
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If you just see a `Page not found` error, it might be because your
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Docker Engine is running on a different machine. This can be the case if:
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- you are using the Docker Toolbox
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- you are using a VM (local or remote) created with Docker Machine
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- you are controlling a remote Docker Engine
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When you run DockerCoins in development mode, the web UI static files
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are mapped to the container using a volume. Alas, volumes can only
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work on a local environment, or when using Docker4Mac or Docker4Windows.
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How to fix this?
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Edit `dockercoins.yml` and comment out the `volumes` section, and try again.
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---
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class: extra-details
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## Why does the speed seem irregular?
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- It *looks like* the speed is approximately 4 hashes/second
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- Or more precisely: 4 hashes/second, with regular dips down to zero
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- Why?
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--
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class: extra-details
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- The app actually has a constant, steady speed: 3.33 hashes/second
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<br/>
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(which corresponds to 1 hash every 0.3 seconds, for *reasons*)
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- Yes, and?
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---
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class: extra-details
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## The reason why this graph is *not awesome*
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- The worker doesn't update the counter after every loop, but up to once per second
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- The speed is computed by the browser, checking the counter about once per second
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- Between two consecutive updates, the counter will increase either by 4, or by 0
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- The perceived speed will therefore be 4 - 4 - 4 - 0 - 4 - 4 - 0 etc.
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- What can we conclude from this?
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--
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class: extra-details
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- "I'm clearly incapable of writing good frontend code!"😀 --Jérôme
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