API Gateway

Neil Haddley • February 10, 2021

How to publish a collection of microservices using an API Gateway.

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Client applications can be configured to connect to services directly.

Client applications can be configured to connect to services via a gateway.

A client might be a web page running in a browser or a mobile phone app.

The diagram above demonstrates how an API gateway sits between a client and a collection of services.

An API Gateway introduces latency but provides a number of benefits:

- Improved security - User authentication and other security tasks can be managed in one place

- Better metrics - Since all traffic flows through the gateway it is easier to add instrumentation

- Simpler code - With the gateway managing security and metrics centrally each service is easier to write

nginx

Here we use nginx as the basis of our reverse proxy. In the Docker file we specify that the /etc/nginx/conf.d/default.conf file in the nginx image will be replaced by a custom my-server.config

DOCKERFILE
1FROM nginx
2COPY ./my-server.conf /etc/nginx/conf.d/default.conf
3EXPOSE 80

Reverse proxy

The proxied server URLs are set using the proxy_pass directive.

NGINX
1server {
2  listen 80;
3  
4  default_type text/plain;
5
6  location / {
7    proxy_pass http://books-react-service:3000;
8  }
9
10  location /books {
11    proxy_pass http://books-service:5000;
12  }
13
14}

Kubernetes

Kubernetes is a platform for managing containerized workloads.

The yaml file below ensures that there are two copies of the books image, two copies of the books-react image and one copy of the books-reverse-proxy image running at all times.

The books-reverse-proxy image is the API Gateway.

The yaml file below ensures that clients are only able to connect to the API Gateway.

The books container image provides a REST API Service.

The books-react container image provides a React App.

YAML
1apiVersion: apps/v1
2kind: Deployment
3metadata:
4  name: books-deployment
5  labels:
6    app: books
7spec:
8  replicas: 2
9  selector:
10    matchLabels:
11      app: books
12  template:
13    metadata:
14      labels:
15        app: books
16    spec:
17      containers:
18        - name: books
19          image: haddley/books
20          ports:
21            - containerPort: 5000
22---
23apiVersion: v1
24kind: Service
25metadata:
26  name: books-service
27spec:
28  selector:
29    app: books
30  ports:
31    - protocol: TCP
32      port: 5000
33      targetPort: 5000
34  type: ClusterIP
35---
36apiVersion: apps/v1
37kind: Deployment
38metadata:
39  name: books-react-deployment
40  labels:
41    app: books
42spec:
43  replicas: 2
44  selector:
45    matchLabels:
46      app: books-react
47  template:
48    metadata:
49      labels:
50        app: books-react
51    spec:
52      containers:
53        - name: books-react
54          image: haddley/books-react
55          ports:
56            - containerPort: 3000
57---
58apiVersion: v1
59kind: Service
60metadata:
61  name: books-react-service
62spec:
63  selector:
64    app: books-react
65  ports:
66    - protocol: TCP
67      port: 3000
68      targetPort: 3000
69  type: ClusterIP
70---
71apiVersion: apps/v1
72kind: Deployment
73metadata:
74  name: books-reverse-proxy-deployment
75  labels:
76    app: books-reverse-proxy
77spec:
78  replicas: 1
79  selector:
80    matchLabels:
81      app: books-reverse-proxy
82  template:
83    metadata:
84      labels:
85        app: books-reverse-proxy
86    spec:
87      containers:
88        - name: books-reverse-proxy
89          image: haddley/books-reverse-proxy
90          ports:
91            - containerPort: 80
92---
93apiVersion: v1
94kind: Service
95metadata:
96  name: books-reverse-proxy-service
97spec:
98  selector:
99    app: books-reverse-proxy
100  ports:
101    - protocol: TCP
102      port: 80
103      targetPort: 80
104  type: LoadBalancer

Kubernetes Hosting

Kubernetes hosting is offered by Microsoft (Azure), Amazon (AWS) and Google (Google Cloud).

Kubernetes can be run on a developer's laptop using Docker Desktop or Minikube.

Kubernetes can be run on a collection of Raspberry Pi computers using K3s.

Shown below is a copy of Docker Desktop hosting the Kubernetes cluster described above.

Docker Desktop

Docker Desktop