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An Introduction to Service Mesh

A simple Web UI: videos-web


Consider videos-web
It's an HTML application that lists a bunch of playlists with videos in them.

+------------+
| videos-web |
|            |
+------------+

A simple API: playlists-api


For videos-web to get any content, it needs to make a call to playlists-api

+------------+     +---------------+
| videos-web +---->+ playlists-api |
|            |     |               |
+------------+     +---------------+

Playlists consist of data like title, description etc, and a list of videos.
Playlists are stored in a database.
playlists-api stores its data in a database

+------------+     +---------------+    +--------------+
| videos-web +---->+ playlists-api +--->+ playlists-db |
|            |     |               |    |              |
+------------+     +---------------+    +--------------+

A little complexity


Each playlist item contains only a list of video id's.
A playlist does not have the full metadata of each video.

Example playlist:

{
  "id" : "playlist-01",
  "title": "Cool playlist",
  "videos" : [ "video-1", "video-x" , "video-b"]
}

Take not above videos: [] is a list of video id's

Videos have their own title and description and other metadata.

To get this data, we need a videos-api
This videos-api has its own database too 

+------------+       +-----------+
| videos-api +------>+ videos-db |
|            |       |           |
+------------+       +-----------+

For the playlists-api to load all the video data, it needs to call videos-api for each video ID it has.

Traffic flow


A single `GET` request to the `playlists-api` will get all the playlists from its database with a single DB call

For every playlist and every video in each list, a separate GET call will be made to the videos-api which will retrieve the video metadata from its database.

This will result in many network fanouts between playlists-api and videos-api and many call to its database.
This is intentional to demonstrate a busy network.


Full application architecture



+------------+     +---------------+    +--------------+
| videos-web +---->+ playlists-api +--->+ playlists-db |
|            |     |               |    |              |
+------------+     +-----+---------+    +--------------+
                         |
                         v
                   +-----+------+       +-----------+
                   | videos-api +------>+ videos-db |
                   |            |       |           |
                   +------------+       +-----------+

Adding an Ingress Controller

Adding an ingress controller allows us to route all our traffic.
We setup a host file with entry 127.0.0.1 servicemesh.demo And port-forward to the ingress-controller

servicemesh.demo/home --> videos-web
servicemesh.demo/api/playlists --> playlists-api


                              servicemesh.demo/home/           +--------------+
                              +------------------------------> | videos-web   |
                              |                                |              |
servicemesh.demo/home/ +------+------------+                   +--------------+
   +------------------>+ingress-nginx      |
                       |Ingress controller |
                       +------+------------+                   +---------------+    +--------------+
                              |                                | playlists-api +--->+ playlists-db |
                              +------------------------------> |               |    |              |
                              servicemesh.demo/api/playlists   +-----+---------+    +--------------+
                                                                     |
                                                                     v
                                                               +-----+------+       +-----------+
                                                               | videos-api +------>+ videos-db |
                                                               |            |       |           |
                                                               +------------+       +-----------+

Run the apps: Docker


There is a `docker-compose.yaml` in this directory.
Change your terminal to this folder and run: 
docker-compose build

docker-compose up

You can access the app on http://localhost


Run the apps: Kubernetes


Create a cluster with kind

kind create cluster --name servicemesh --image kindest/node:v1.18.4

Deploy videos-web


cd ./kubernetes/servicemesh/

kubectl apply -f applications/videos-web/deploy.yaml
kubectl port-forward svc/videos-web 80:80

You should see blank page at http://localhost/
It's blank because it needs the playlists-api to get data


Deploy playlists-api and database


cd ./kubernetes/servicemesh/

kubectl apply -f applications/playlists-api/deploy.yaml
kubectl apply -f applications/playlists-db/
kubectl port-forward svc/playlists-api 81:80

You should see empty playlists page at http://localhost/
Playlists are empty because it needs the videos-api to get video data


Deploy videos-api and database


cd ./kubernetes/servicemesh/

kubectl apply -f applications/videos-api/deploy.yaml
kubectl apply -f applications/videos-db/

Refresh page at http://localhost/
You should now see the complete architecture in the browser