Course Introduction

What You'll Learn in This Course

Golang Useful Resources and Tools

The authors

The history of Go

Installing Go

Golang: An Overview of Fundamental Concepts

Introduction

A Quick Primer on Key-Value Servers and Hash Tables

How to Create a Basic hello world Webserver with Go

Build a Basic hello world JSON API Server with Go + Chi

How to Create an In-Memory Hash Table API with Go + Chi

Conclusion

A key-value server

Testing a key-value server

What is End-to-End Testing, Integration Testing, and Unit Testing?

Writing Unit Tests for JSON Functions in Go

Parallel Testing in Golang: How to Use t.Parallel()

A Brief Overview of Golang Benchmarks

Integration testing

Further testing types

Distributed key-value server

What is Distributed Consensus and How Does it Work?

An Introduction to Using Raft for Distributed Consensus

Create a Distributed Webserver using Golang and Raft

Connecting Golang Servers With a Handler and Middleware

Building a Store Package to Sync Data in Go with Raft's FSM

Testing Distributed Golang Webservers in Docker Containers

Distributed Key Value Server

Monitoring

White Box Monitoring vs Black Box Monitoring

A Introduction to Golang Logging

Defining and Implementing Distributed System Tracing with Go

Alerting

Understanding the Basics of Canary Deployments

Wait, what's a load balancer?

What aren't we doing?

So what will we be doing?

How to Create a Basic Random-per-request Load Balancer

What is Weighted Round Robin Load Balancing?

Streamlining Configuration Updates for Canary Deployments

Other considerations

Three Open-Source Load Balancers Written in Go

A canary deployment server

Chat server

Chatting about chat servers

What features don't we want (yet)?

What features do we want?

Using a SQLite database in Golang

How to Create an API for a Golang Chat Server

Creating a Frontend Interface in Go for a Chat Server

How to Deploy a Golang Webserver With Docker

Future improvements

Future thinking

Project ideas

Areas of more research

In this book we will show you the some of the concerns of backend web development through the lens of Go.

It is taught by Nat Welch (formerly an SRE at Google) and Steve McCarthy (Etsy), two Go developers who have been writing software for more than 25 years combined.

In the course, we'll be covering the creation and concerns of a number of fundamental backend building blocks or larger applications:

- A key value server, including the use of distributed consensus algorithms
- A canary deployment server
- A real time chat service
- Testing and monitoring

Regardless of your background, Go can make you a _better backend developer_, but learning Go is challenging because the language looks simple on the outside, but you won't get its full benefit unless you know what it can _really_ do. 

**By the end of the first chapter, you'll already _have built a key-value server reminiscent of similar systems like Redis and memcached._** The subsequent chapters will dive into more hands-on projects and Go concepts including:

- How to test your Go systems with unit tests and integration tests
- **Project**: create a **distributed version of the key-value server** in order to solve the typical problems of server systems such as _node failure_
- How to solve the **problem of "consensus"** in distributed Go systems
- How to write code to **keep data in sync** when running a system for servers located around the globe
- Implementing **black box and white box monitoring** systems for Go servers
- **Project**: building a **load balancer server** from scratch
- Why and how to implement a **canary deployment server** for bug-free gradual deployments
- How to build a **configuration server** to allow zero-downtime deploys 
- Understanding the various tradeoffs in the **design decisions** for Go server systems
- **Project**: build a Go chat server system from the ground up 
- **Database modeling** for backend development as part of your chat server project
- **and a lot more**...

## A Key-Value Server Like Redis And Memcached

n the early chapters of the book we learn how to build a Golang version of a key-value server that works in a manner similar to Redis and Memcached. You'll implement each of these features in Go:

- set and retrieve values by key
- adding persistent storage
- using data encodings such as `JSON` and `base64`
- testing the server with unit tests and integration tests

In these chapters, we also learn how to build a more advanced solution for the problem: **a distributed version of the key-value server**. You will learn how to use **consensus algorithms** in Go to solve the problem of keeping distributed servers in sync. The solid grounding you get in programming Go in these first chapters readies you for more complex Go projects.

## A Real-Time Chat Service

A real-time chat server implemented in Go gives you the opportunity to bring together systems thinking as well as concerns common for web apps:

- relational data modeling with SQL
- authentication
- implementing RESTful resources

Working through this comprehensive project will give you **a high degree of confidence about using Go to implement a huge project from scratch**. You will feel ready to use Go with relational databases such as PostgreSQL or MySQL, and databases in general.

## A Canary Deployment Server And Load Balancer

The work you do in the chapters covering building a canary deployment server and load balancer will open your eyes to the full power of Go. Gradual deployments are a commonly used strategy for code deployments, and the projects you build in these chapters get you familiar with building this kind of **infrastructure software**. 

Your load balancer will implement _random-per-request_ as well as _round-robin_ load balancing. These projects will give you a thorough immersion in systems problem solving with Go. You'll be able to show off your skills on bold projects of your own, in job interviews, and on the job when collaborating with colleagues.

## This book is the _fastest_ way to learn modern backend Go development

With _The newline Guide to Reliable Webservers with Go_, you won't waste time reading shallow blog posts that can't go beyond showing you the simplest Go examples or Todo apps. Instead, **within the first chapter** you'll be well on your way to creating a **Redis-like key-value server**, and the complexity of the systems you're able to build only accelerates from there.

This book opens the door to **more effective backend development** and utilizing the full power of Golang for **microservices**. As Go transforms the systems development landscape, you can use this book and the skills it teaches you to contribute to a faster, more effective systems development experience for your team.

With _The newline Guide to Reliable Webservers with Go_ you can **go from novice to proficiency in Go in a predictable way, without wasting time, and without picking up bad Go coding habits**.

So grab a copy now to advance your journey with Go.

In this book we show important concepts in backend web development through the lens of Go.

Reliable Webservers with Go

The importance of testing your web servers

How to apply distributed consensus algorithms to your key value server

We are now starting to make our key-value server. Using our hello world server that returns JSON as a base, we can extend it with all the rest of the pieces a key-value server needs.

We can start adding handlers for our basic business logic. We will need three essential functions:

r.Get("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")

	data, err := Get(r.Context(), key)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	w.Write([]byte(data))
})

 handler. It has three things worth talking about.

 function. This is like saying "for every request URL that starts with /key/, send it to this handler, with the variable key containing everything after the second slash". The handler in this case is the second argument to 

 - an anonymous function which matches type of a 

This is a feature of Chi, as Get is a function of Chi's router. Sadly, Go is a very explicit language, so if you're used to Ruby or JavaScript which just might make a magic variable available, this might come as a shock, but in Go, you must ask for the variable. So the first line in the function, we get the data from the request URL and save it to a local variable with 

A lot of developers might immediately take this variable and do data validation on this incoming key. This is important, but we will save that for later, because we are just going to call a yet-to-be defined function named 

, which will do the actual work of getting the data. We do this so we can separate concerns. The web server code is distinct from the key/value storage code.

 function call brings us to the second thing we want to talk about, 

. Context was introduced into Go around version 

. Context is a concept that carries request-scoped data with it. We could add a timeout or extra tracing data to our program, and with context, it is plumed all the way through. Each function that receives a context is in charge of dealing with it, and also not harming the package-scoped variables shoved in there. Mostly Go deals with this for us, and you'll find most modern Go libraries deal with context correctly. To start with, we won't do anything with the context, but leave it there so we can easily pass through data later.

The third thing to talk about is the error handling. We skipped over this in the JSON function, but we will address it now. The Get function, like many things in Go, returns both data and an error. This tends to confuse many programmers used to languages with throw or raise exception functionality. Go doesn't have that. Instead it passes around an instance of the error type. If it is nil, data is good, and if it is not nil, there was an error and you need to handle it. In this case, we are setting the status code to 500 (which is what the constant 

 equals), and then returning a JSON blob to the user with the string inside the error.

 handler, which responds to an HTTP DELETE verb instead of the GET verb, we can see it looks almost identical. This should be added after our 

r.Delete("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")

	err := Delete(r.Context(), key)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	JSON(w, map[string]string{"status": "success"})
})

Finally, we will need to be able to set values, which we will do with a 

 handler, dealing with POST requests, which looks similar, but slightly different, as we will need to parse the POST request body. Put this after the 

r.Post("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")
	body, err := io.ReadAll(r.Body)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	err = Set(r.Context(), key, string(body))
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	JSON(w, map[string]string{"status": "success"})
})

 which simplifies the act of reading from a buffer via 

. There are downsides to this, such as not being able to check buffer sizes before reading into memory, but for our case right now, we can let it slide. In the future we might want to put a maximum value size, in which case we might want to modify this line.

. If you are using a version of Go that is older than 1.16, you'll quickly find out that this function doesn't exist. That is because it exists in a package called 

 has a bunch of convenient functions for reading and writing to files, but the package itself isn't the obvious place for any of these functions. So in go 1.16 they were split between the 

The rest of the function is pretty close to Get and Delete. The only additional thing we are doing is casting the request body from 

---
title: "How to Create an In-Memory Hash Table API with Go + Chi"
# description: desc
# privateVideoUrl: url
code: https://gitlab.com/fullstackio/books/newline-course-apps/nat-welch-and-steve-mcarthy-reliable-webservers-in-go-app/-/tree/main/code/key-value-store/lesson_02.03
---

# Creating an in-memory hash table API

We are now starting to make our key-value server. Using our hello world server that returns JSON as a base, we can extend it with all the rest of the pieces a key-value server needs.

### Basic handlers Get, Set & Delete

We can start adding handlers for our basic business logic. We will need three essential functions:

-   **Get** a value by key
-   **Set** a key with a value
-   **Delete** a key

Put this below the existing `r.Get("/" ...)` section within the `main` func.

```go
r.Get("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")

	data, err := Get(r.Context(), key)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	w.Write([]byte(data))
})
```

Let's begin with the **Get** handler. It has three things worth talking about.

First is the URL pattern: `"/key/{key}"`, which is the first argument to the `r.Get` function. This is like saying "for every request URL that starts with /key/, send it to this handler, with the variable key containing everything after the second slash". The handler in this case is the second argument to `r.Get` - an anonymous function which matches type of a `http.HandlerFunc`.

This is a feature of Chi, as Get is a function of Chi's router. Sadly, Go is a very explicit language, so if you're used to Ruby or JavaScript which just might make a magic variable available, this might come as a shock, but in Go, you must ask for the variable. So the first line in the function, we get the data from the request URL and save it to a local variable with `key := chi.URLParam(r, "key")`.

A lot of developers might immediately take this variable and do data validation on this incoming key. This is important, but we will save that for later, because we are just going to call a yet-to-be defined function named `Get()`, which will do the actual work of getting the data. We do this so we can separate concerns. The web server code is distinct from the key/value storage code.

This `Get()` function call brings us to the second thing we want to talk about, `r.Context()`. Context was introduced into Go around version [1.7 in 2014](https://blog.golang.org/context). Context is a concept that carries request-scoped data with it. We could add a timeout or extra tracing data to our program, and with context, it is plumed all the way through. Each function that receives a context is in charge of dealing with it, and also not harming the package-scoped variables shoved in there. Mostly Go deals with this for us, and you'll find most modern Go libraries deal with context correctly. To start with, we won't do anything with the context, but leave it there so we can easily pass through data later.

The third thing to talk about is the error handling. We skipped over this in the JSON function, but we will address it now. The Get function, like many things in Go, returns both data and an error. This tends to confuse many programmers used to languages with throw or raise exception functionality. Go doesn't have that. Instead it passes around an instance of the error type. If it is nil, data is good, and if it is not nil, there was an error and you need to handle it. In this case, we are setting the status code to 500 (which is what the constant `http.StatusInternalServerError` equals), and then returning a JSON blob to the user with the string inside the error.

That's it, now we have a basic `Get` handler!

If we look at the **Delete** handler, which responds to an HTTP DELETE verb instead of the GET verb, we can see it looks almost identical. This should be added after our `r.Get` handler from above.

```go
r.Delete("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")

	err := Delete(r.Context(), key)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	JSON(w, map[string]string{"status": "success"})
})
```

Finally, we will need to be able to set values, which we will do with a **Set** handler, dealing with POST requests, which looks similar, but slightly different, as we will need to parse the POST request body. Put this after the `r.Delete` handler we just added.

```go
r.Post("/key/{key}", func(w http.ResponseWriter, r *http.Request) {
	key := chi.URLParam(r, "key")
	body, err := io.ReadAll(r.Body)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}

	err = Set(r.Context(), key, string(body))
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		JSON(w, map[string]string{"error": err.Error()})
		return
	}