Add 2023 day 84 What is an API

Signed-off-by: Alistair Hey <alistair@heyal.co.uk>

2023.md

@@ -156,7 +156,7 @@ Or contact us via Twitter, my handle is [@MichaelCade1](https://twitter.com/Mich
 
 ### Engineering for Day 2 Ops
 
-- [] 👷🏻‍♀️ 84 > [](2023/day84.md)
+- [✔] 👷🏻‍♀️ 84 > [Writing an API - What is an API?](2023/day84.md)
 - [] 👷🏻‍♀️ 85 > [](2023/day85.md)
 - [] 👷🏻‍♀️ 86 > [](2023/day86.md)
 - [] 👷🏻‍♀️ 87 > [](2023/day87.md)

2023/day2-ops-code/README.md

@@ -0,0 +1,44 @@
+# Getting started
+
+This repo expects you to have a working kubernetes cluster already setup and
+available with kubectl
+
+We expect you already have a kubernetes cluster setup and available with kubectl and helm.
+
+I like using (Civo)[https://www.civo.com/] for this as it is easy to setup and run clusters
+
+The code is available in this folder to build/push your own images if you wish - there are no instructions for this.
+
+## Start the Database
+```shell
+kubectl apply -f database/mysql.yaml
+```
+
+
+## deploy the day1 - sync
+```shell
+kubectl apply -f synchronous/k8s.yaml
+```
+
+Check your logs 
+```shell 
+kubectl logs deploy/generator
+
+kubectl logs deploy/requestor
+```
+
+## deploy nats
+helm repo add nats https://nats-io.github.io/k8s/helm/charts/
+helm install my-nats nats/nats
+
+## deploy day 2 - async
+```shell
+kubectl apply -f async/k8s.yaml
+```
+
+Check your logs
+```shell 
+kubectl logs deploy/generator
+
+kubectl logs deploy/requestor
+```

2023/day2-ops-code/database/mysql.yaml

@@ -0,0 +1,77 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: mysql
+spec:
+  ports:
+    - port: 3306
+  selector:
+    app: mysql
+  clusterIP: None
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: mysql
+spec:
+  selector:
+    matchLabels:
+      app: mysql
+  strategy:
+    type: Recreate
+  template:
+    metadata:
+      labels:
+        app: mysql
+    spec:
+      containers:
+        - image: mysql:5.6
+          name: mysql
+          env:
+            # Use secret in real usage
+            - name: MYSQL_ROOT_PASSWORD
+              value: password
+            - name: MYSQL_DATABASE
+              value: example
+            - name: MYSQL_USER
+              value: example
+            - name: MYSQL_PASSWORD
+              value: password
+          ports:
+            - containerPort: 3306
+              name: mysql
+          volumeMounts:
+            - name: mysql-persistent-storage
+              mountPath: /var/lib/mysql
+      volumes:
+        - name: mysql-persistent-storage
+          persistentVolumeClaim:
+            claimName: mysql-pv-claim
+---
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  name: mysql-pv-volume
+  labels:
+    type: local
+spec:
+  storageClassName: manual
+  capacity:
+    storage: 20Gi
+  accessModes:
+    - ReadWriteOnce
+  hostPath:
+    path: "/mnt/data"
+---
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mysql-pv-claim
+spec:
+  storageClassName: manual
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 10Gi
+# https://kubernetes.io/docs/tasks/run-application/run-single-instance-stateful-application/

2023/day2-ops-code/synchronous/generator/Dockerfile

@@ -0,0 +1,17 @@
+# Set the base image to use
+FROM golang:1.17-alpine
+
+# Set the working directory inside the container
+WORKDIR /app
+
+# Copy the source code into the container
+COPY . .
+
+# Build the Go application
+RUN go build -o main .
+
+# Expose the port that the application will run on
+EXPOSE 8080
+
+# Define the command that will run when the container starts
+CMD ["/app/main"]

2023/day2-ops-code/synchronous/generator/go.mod

@@ -0,0 +1,5 @@
+module main
+
+go 1.20
+
+require github.com/go-sql-driver/mysql v1.7.0

2023/day2-ops-code/synchronous/generator/go.sum

@@ -0,0 +1,2 @@
+github.com/go-sql-driver/mysql v1.7.0 h1:ueSltNNllEqE3qcWBTD0iQd3IpL/6U+mJxLkazJ7YPc=
+github.com/go-sql-driver/mysql v1.7.0/go.mod h1:OXbVy3sEdcQ2Doequ6Z5BW6fXNQTmx+9S1MCJN5yJMI=

2023/day2-ops-code/synchronous/generator/main.go

@@ -0,0 +1,139 @@
+package main
+
+import (
+	"database/sql"
+	"fmt"
+	_ "github.com/go-sql-driver/mysql"
+	"math/rand"
+	"net/http"
+	"time"
+)
+
+func generateAndStoreString() (string, error) {
+	// Connect to the database
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	if err != nil {
+		return "", err
+	}
+	defer db.Close()
+
+	// Generate a random string
+	// Define a string of characters to use
+	characters := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+
+	// Generate a random string of length 10
+	randomString := make([]byte, 64)
+	for i := range randomString {
+		randomString[i] = characters[rand.Intn(len(characters))]
+	}
+
+	// Insert the random number into the database
+	_, err = db.Exec("INSERT INTO generator(random_string) VALUES(?)", string(randomString))
+	if err != nil {
+		return "", err
+	}
+
+	fmt.Printf("Random string %s has been inserted into the database\n", string(randomString))
+	return string(randomString), nil
+}
+
+func main() {
+	// Create a new HTTP server
+	server := &http.Server{
+		Addr: ":8080",
+	}
+
+	err := createGeneratordb()
+	if err != nil {
+		panic(err.Error())
+	}
+
+	ticker := time.NewTicker(60 * time.Second)
+	quit := make(chan struct{})
+	go func() {
+		for {
+			select {
+			case <-ticker.C:
+				checkStringReceived()
+			case <-quit:
+				ticker.Stop()
+				return
+			}
+		}
+	}()
+
+	// Handle requests to /generate
+	http.HandleFunc("/new", func(w http.ResponseWriter, r *http.Request) {
+		// Generate a random number
+		randomString, err := generateAndStoreString()
+		if err != nil {
+			http.Error(w, "unable to generate and save random string", http.StatusInternalServerError)
+			return
+		}
+
+		print(fmt.Sprintf("random string: %s", randomString))
+		w.Write([]byte(randomString))
+	})
+
+	// Start the server
+	fmt.Println("Listening on port 8080")
+	err = server.ListenAndServe()
+	if err != nil {
+		panic(err.Error())
+	}
+}
+
+func createGeneratordb() error {
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+
+	// try to create a table for us
+	_, err = db.Exec("CREATE TABLE IF NOT EXISTS generator(random_string VARCHAR(100), seen BOOLEAN)")
+
+	return err
+}
+
+func checkStringReceived() {
+	// get a list of strings from database that dont have the "seen" bool set top true
+	// loop over them and make a call to the requestor's 'check' endpoint and if we get a 200 then set seen to true
+
+	// Connect to the database
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	if err != nil {
+		print(err)
+	}
+	defer db.Close()
+
+	// Insert the random number into the database
+	results, err := db.Query("SELECT random_string FROM generator WHERE seen IS NOT true")
+	if err != nil {
+		print(err)
+	}
+
+	// loop over results
+	for results.Next() {
+		var randomString string
+		err = results.Scan(&randomString)
+		if err != nil {
+			print(err)
+		}
+
+		// make a call to the requestor's 'check' endpoint
+		// if we get a 200 then set seen to true
+		r, err := http.Get("http://requestor-service:8080/check/" + randomString)
+		if err != nil {
+			print(err)
+		}
+		if r.StatusCode == 200 {
+			_, err = db.Exec("UPDATE generator SET seen = true WHERE random_string = ?", randomString)
+			if err != nil {
+				print(err)
+			}
+		} else {
+			fmt.Println(fmt.Sprintf("Random string has not been received by the requestor: %s", randomString))
+		}
+	}
+}

2023/day2-ops-code/synchronous/k8s.yaml

@@ -0,0 +1,69 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: requestor
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: requestor
+  template:
+    metadata:
+      labels:
+        app: requestor
+    spec:
+      containers:
+        - name: requestor
+          image: heyal/requestor:sync
+          imagePullPolicy: Always
+          ports:
+            - containerPort: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: requestor-service
+spec:
+  selector:
+    app: requestor
+  ports:
+    - name: http
+      protocol: TCP
+      port: 8080
+      targetPort: 8080
+  type: ClusterIP
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: generator
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: generator
+  template:
+    metadata:
+      labels:
+        app: generator
+    spec:
+      containers:
+        - name: generator
+          image: heyal/generator:sync
+          imagePullPolicy: Always
+          ports:
+            - containerPort: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: generator-service
+spec:
+  selector:
+    app: generator
+  ports:
+    - name: http
+      protocol: TCP
+      port: 8080
+      targetPort: 8080
+  type: ClusterIP

2023/day2-ops-code/synchronous/requestor/Dockerfile

@@ -0,0 +1,17 @@
+# Set the base image to use
+FROM golang:1.17-alpine
+
+# Set the working directory inside the container
+WORKDIR /app
+
+# Copy the source code into the container
+COPY . .
+
+# Build the Go application
+RUN go build -o main .
+
+# Expose the port that the application will run on
+EXPOSE 8080
+
+# Define the command that will run when the container starts
+CMD ["/app/main"]

2023/day2-ops-code/synchronous/requestor/go.mod

@@ -0,0 +1,5 @@
+module main
+
+go 1.20
+
+require github.com/go-sql-driver/mysql v1.7.0

2023/day2-ops-code/synchronous/requestor/go.sum

@@ -0,0 +1,2 @@
+github.com/go-sql-driver/mysql v1.7.0 h1:ueSltNNllEqE3qcWBTD0iQd3IpL/6U+mJxLkazJ7YPc=
+github.com/go-sql-driver/mysql v1.7.0/go.mod h1:OXbVy3sEdcQ2Doequ6Z5BW6fXNQTmx+9S1MCJN5yJMI=

2023/day2-ops-code/synchronous/requestor/main.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	_ "github.com/go-sql-driver/mysql"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+func storeString(input string) error {
+	// Connect to the database
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	defer db.Close()
+	// Insert the random number into the database
+	_, err = db.Exec("INSERT INTO requestor(random_string) VALUES(?)", input)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Random string %s has been inserted into the database\n", input)
+	return nil
+}
+
+func getStringFromDB(input string) error {
+	// see if the string exists in the db, if so return nil
+	// if not, return an error
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	defer db.Close()
+	result, err := db.Query("SELECT * FROM requestor WHERE random_string = ?", input)
+	if err != nil {
+		return err
+	}
+
+	for result.Next() {
+		var randomString string
+		err = result.Scan(&randomString)
+		if err != nil {
+			return err
+		}
+		if randomString == input {
+			return nil
+		}
+	}
+
+	return errors.New("string not found")
+}
+
+func getStringFromGenerator() {
+	// make a request to the generator
+	// save sthe string to db
+	r, err := http.Get("http://generator-service:8080/new")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	fmt.Println(fmt.Sprintf("body from generator: %s", string(body)))
+
+	storeString(string(body))
+
+}
+
+func main() {
+	// setup a goroutine loop calling the generator every minute, saving the result in the DB
+
+	ticker := time.NewTicker(60 * time.Second)
+	quit := make(chan struct{})
+	go func() {
+		for {
+			select {
+			case <-ticker.C:
+				getStringFromGenerator()
+			case <-quit:
+				ticker.Stop()
+				return
+			}
+		}
+	}()
+
+	// Create a new HTTP server
+	server := &http.Server{
+		Addr: ":8080",
+	}
+
+	err := createRequestordb()
+	if err != nil {
+		panic(err.Error())
+	}
+
+	// Handle requests to /generate
+	http.HandleFunc("/check/", func(w http.ResponseWriter, r *http.Request) {
+		// get the value after check from the url
+		id := strings.TrimPrefix(r.URL.Path, "/check/")
+
+		// check if it exists in the db
+		err := getStringFromDB(id)
+		if err != nil {
+			http.Error(w, "string not found", http.StatusNotFound)
+			return
+		}
+
+		fmt.Fprintf(w, "string found", http.StatusOK)
+	})
+
+	// Start the server
+	fmt.Println("Listening on port 8080")
+	err = server.ListenAndServe()
+	if err != nil {
+		panic(err.Error())
+	}
+}
+
+func createRequestordb() error {
+	db, err := sql.Open("mysql", "root:password@tcp(mysql:3306)/mysql")
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+
+	// try to create a table for us
+	_, err = db.Exec("CREATE TABLE IF NOT EXISTS requestor(random_string VARCHAR(100))")
+
+	return err
+}

2023/day84.md

@@ -0,0 +1,58 @@
+# Writing an API - What is an API? 
+
+The acronym API stands for “application programming interface”. What does this really mean though? It’s a way of
+controlling an application programmatically. So when you use a website that displays some data to you (like Twitter)
+there will be an action taken by the interface to get data or send data to the application (the twitter backend in this
+example) - this is done programmatically in the background by code running in the user interface.
+
+In the example given above we looked at an example of a public API, however the vast majority of APIs are private, one
+request to the public twitter API will likely cause a cascade of interactions between programs in the backend. These
+could be to save the tweet text into a datastore, to update the number of likes or views a tweet has or to take an image
+that has been uploaded and resize it for a better viewing experience.
+
+We build programs with APIs that other people can call so that we can expose program logic to other developers, teams
+and our customers or suppliers. They are a predefined way of sharing information. For example, we can define an API
+using [openapi specification](https://swagger.io/resources/open-api/) which is used
+for [RESTful](https://en.wikipedia.org/wiki/Representational_state_transfer) API design. This api specification forms a
+contract that we can fulfil. For example, If you make an API request to me and pass a specific set of content, such as a
+date range, I will respond with a specific set of data. Therefore you can reliably expect to receive data of a certain
+type when calling my API.
+
+We are going to build up an example set of applications that communicate using an API for this section of the learning
+journey to illustrate the topics and give you a hands-on look at how things can be done.
+
+Design:
+2 programs that communicate bi-directionally, every minute or so one application will request a random string from the
+other, once one is received it will store this number in a database for future use
+
+The Random Number generator will generate a random string when requested and save this into a database, the application
+will then ask the first program for confirmation that it received the string, and store this information against the
+string in the database
+
+The applications will be called:
+generator
+requestor
+
+This may sound like a silly example but it allows us to quickly look into the various tasks involved with building,
+deploying, monitoring and owning a service that runs in production. There are bi-directional failure modes as each
+application needs something from the other to complete successfully and things we can monitor such as API call rates -
+We can see if one application stops running.
+
+We need to now decide what our API Interfaces should look like. We have 2 API calls that will be used to communicate
+here. Firstly, the `requestor` will call the `generator` and ask for a string. This is likely going to be an API call
+without any additional content other than making a request for a string. Secondly, the `generator` will start to ask
+the `requestor` for confirmation that it received and stored the string, in this case we need to pass a parameter to
+the `requestor` which will be the string we are interested in knowing about.
+
+The `generator` will use a URL path of `/new` to serve up random strings
+The `requestor` is going to use URL paths to receive string information from the `generator` to check the status, so we
+will setup a URL of `/strings/<STRING>` where <STRING> is the string of interest.
+
+
+## Building the API
+There is a folder on the Github repository  under the 2023 section called `day2-ops-code` and we will be using this 
+folder to store our code for this, and future, section of the learning journey.
+
+We are using Golang's built in HTTP server to serve up our endpoints and asynchronous goroutines to handle the 
+checks. Every 60 seconds we will look into the generators database and get all the strings which we dont have 
+conformation for and then calling the requesters endpoint to check if the string is there.