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146 lines
3.8 KiB
Markdown
146 lines
3.8 KiB
Markdown
# Introduction to Distributed Tracing
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<a href="https://youtu.be/idDu_jXqf4E" title="tracing-intro"><img src="https://i.ytimg.com/vi/idDu_jXqf4E/hqdefault.jpg" width="20%" alt="tracing-intro" /></a>
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In this episode we take a look at distributed tracing.
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We'll take a look at the concept, what distributed tracing is, what problems it solves, how to emit traces and the platform architecture to collect traces.
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## Example microservice architecture
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First of all, we need an example application.
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In this demo, I have a few microservices that work together to form a video catalog.
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## A simple Web UI: videos-web
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<hr/>
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<br/>
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Consider `videos-web` <br/>
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It's an HTML application that lists a bunch of playlists with videos in them.
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```
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+------------+
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| videos-web |
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+------------+
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```
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<br/>
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## A simple API: playlists-api
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<hr/>
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<br/>
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For `videos-web` to get any content, it needs to make a call to `playlists-api`
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```
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+------------+ +---------------+
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| videos-web +---->+ playlists-api |
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| | | |
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+------------+ +---------------+
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```
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Playlists consist of data like `title`, `description` etc, and a list of `videos`. <br/>
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Playlists are stored in a database. <br/>
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`playlists-api` stores its data in a database
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```
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+------------+ +---------------+ +--------------+
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| videos-web +---->+ playlists-api +--->+ playlists-db |
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| | | | | |
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+------------+ +---------------+ +--------------+
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```
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<br/>
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## A little complexity
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<hr/>
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<br/>
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Each playlist item contains only a list of video id's. <br/>
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A playlist does not have the full metadata of each video. <br/>
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Example `playlist`:
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```
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{
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"id" : "playlist-01",
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"title": "Cool playlist",
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"videos" : [ "video-1", "video-x" , "video-b"]
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}
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```
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Take not above `videos: []` is a list of video id's <br/>
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Videos have their own `title` and `description` and other metadata. <br/>
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To get this data, we need a `videos-api` <br/>
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This `videos-api` has its own database too <br/>
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```
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+------------+ +-----------+
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| videos-api +------>+ videos-db |
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+------------+ +-----------+
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```
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For the `playlists-api` to load all the video data, it needs to call `videos-api` for each video ID it has.<br/>
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<br/>
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## Traffic flow
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<hr/>
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<br/>
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A single `GET` request to the `playlists-api` will get all the playlists
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from its database with a single DB call <br/>
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For every playlist and every video in each list, a separate `GET` call will be made to the `videos-api` which will
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retrieve the video metadata from its database. <br/>
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This will result in many network fanouts between `playlists-api` and `videos-api` and many call to its database. <br/>
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This is intentional to demonstrate a busy network.
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<br/>
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## Full application architecture
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<hr/>
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<br/>
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```
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+------------+ +---------------+ +--------------+
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| videos-web +---->+ playlists-api +--->+ playlists-db |
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| | | | | [redis] |
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+------------+ +-----+---------+ +--------------+
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v
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+-----+------+ +-----------+
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| videos-api +------>+ videos-db |
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| | | [redis] |
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+------------+ +-----------+
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```
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<br/>
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## Run the apps: Docker
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<hr/>
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<br/>
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There is a `docker-compose.yaml` in this directory. <br/>
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Change your terminal to this folder and run:
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```
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cd tracing
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docker-compose build
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docker-compose up
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```
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You can access the app on `http://localhost`. <br/>
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You should now see the complete architecture in the browser
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<br/>
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## Traces
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<hr/>
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<br/>
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To see our traces, we can access the Jaeger UI on `http://localhost:16686` |