Getting Started on Heroku with Go

Introduction

This tutorial will have you deploying a Go app in minutes.

Hang on for a few more minutes to learn how it all works, so you can make the most out of Heroku.

The tutorial assumes that you have:

• A verified Heroku Account
• Go 1.20+ installed
• An Eco dynos plan subscription (recommended)

Set up

In this step you’ll install the Heroku Command Line Interface (CLI). You use the CLI to manage and scale your applications, provision add-ons, view your application logs, and run your application locally.

Download and run the installer for your platform:

Once installed, you can use the heroku command from your command shell.

Use the heroku login command to log in to the Heroku CLI:

$ heroku login
heroku: Press any key to open up the browser to login or q to exit
 ›   Warning: If browser does not open, visit
 ›   https://cli-auth.heroku.com/auth/browser/***
heroku: Waiting for login...
Logging in... done
Logged in as me@example.com

This command opens your web browser to the Heroku login page. If your browser is already logged in to Heroku, simply click the Log in button displayed on the page.

This authentication is required for both the heroku and git commands to work correctly.

Prepare the app

In this step, you will prepare a sample application that’s ready to be deployed to Heroku.

Clone the sample application so that you have a local version of the code that you can then deploy to Heroku, execute the following commands in your local command shell or terminal:

$ git clone https://github.com/heroku/go-getting-started.git
$ cd go-getting-started

You now have a functioning git repository that contains a simple application as well as a go.mod file, which is used by the Go’s module dependency system.

Deploy the app

In this step you will deploy the app to Heroku.

 

Create an app on Heroku, which prepares Heroku to receive your source code.

$ heroku create
Creating polar-inlet-4930... done, stack is heroku-18
https://polar-inlet-4930.herokuapp.com/ | https://git.heroku.com/polar-inlet-4930.git
Git remote heroku added

When you create an app, a git remote (called heroku) is also created and associated with your local git repository.

Heroku generates a random name (in this case polar-inlet-4930) for your app, or you can pass a parameter to specify your own app name.

Now deploy your code:

$ git push heroku main
Enumerating objects: 2483, done.
Counting objects: 100% (2483/2483), done.
Delta compression using up to 16 threads
Compressing objects: 100% (1921/1921), done.
Writing objects: 100% (2483/2483), 12.37 MiB | 6.34 MiB/s, done.
Total 2483 (delta 850), reused 1269 (delta 401), pack-reused 0
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Building on the Heroku-22 stack
remote: -----> Determining which buildpack to use for this app
remote: -----> Go app detected
remote: -----> Fetching jq... done
remote: -----> Fetching stdlib.sh.v8... done
remote: ----->
remote:        Detected go modules via go.mod
remote: ----->
remote:        Detected Module Name: github.com/heroku/go-getting-started
remote: ----->
remote: -----> New Go Version, clearing old cache
remote: -----> Installing go1.20
remote: -----> Fetching go1.20.linux-amd64.tar.gz... done
remote: -----> Determining packages to install
remote:
remote:        Detected the following main packages to install:
remote:                 github.com/heroku/go-getting-started
remote:
remote: -----> Running: go install -v -tags heroku -mod=vendor github.com/heroku/go-getting-started
remote: internal/unsafeheader
remote: internal/goarch
remote: internal/cpu
remote: internal/abi
remote (many more lines of dependendencies truncated)
remote: github.com/gin-gonic/gin
remote: github.com/heroku/go-getting-started
remote:
remote:        Installed the following binaries:
remote:                 ./bin/go-getting-started
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:
remote: -----> Compressing...
remote:        Done: 19.9M
remote: -----> Launching...
remote:        Released v3
remote:        https://polar-inlet-4930.herokuapp.com/ deployed to Heroku
remote:
remote: Verifying deploy... done.
To https://git.heroku.com/polar-inlet-4930.git

The application is now deployed.

Visit the app at the URL generated by its app name.

As a handy shortcut, you can open the website as follows:

$ heroku open

View logs

Heroku treats logs as streams of time-ordered events aggregated from the output streams of all your app and Heroku components, providing a single channel for all of the events.

View information about your running app using one of the logging commands, heroku logs --tail:

$ heroku logs --tail
2023-03-06T17:45:11.483269+00:00 app[api]: Initial release by user jlewis@heroku.com
2023-03-06T17:45:11.483269+00:00 app[api]: Release v1 created by user jlewis@heroku.com
2023-03-06T17:45:11.617923+00:00 app[api]: Enable Logplex by user jlewis@heroku.com
2023-03-06T17:45:11.617923+00:00 app[api]: Release v2 created by user jlewis@heroku.com
2023-03-06T17:46:03.000000+00:00 app[api]: Build started by user jlewis@heroku.com
2023-03-06T17:46:42.719610+00:00 app[api]: Release v3 created by user jlewis@heroku.com
2023-03-06T17:46:42.719610+00:00 app[api]: Deploy 396c5869 by user jlewis@heroku.com
2023-03-06T17:46:42.733628+00:00 app[api]: Scaled to web@1:Basic by user jlewis@heroku.com
2023-03-06T17:46:43.984474+00:00 heroku[web.1]: Starting process with command `go-getting-started`
2023-03-06T17:46:45.283361+00:00 app[web.1]: [GIN-debug] [WARNING] Running in "debug" mode. Switch to "release" mode in production.
2023-03-06T17:46:45.283386+00:00 app[web.1]: - using env:       export GIN_MODE=release
2023-03-06T17:46:45.283386+00:00 app[web.1]: - using code:      gin.SetMode(gin.ReleaseMode)
2023-03-06T17:46:45.283390+00:00 app[web.1]:
2023-03-06T17:46:45.283602+00:00 app[web.1]: [GIN-debug] Loaded HTML Templates (4):
2023-03-06T17:46:45.283602+00:00 app[web.1]: -
2023-03-06T17:46:45.283610+00:00 app[web.1]: - header.tmpl.html
2023-03-06T17:46:45.283610+00:00 app[web.1]: - index.tmpl.html
2023-03-06T17:46:45.283610+00:00 app[web.1]: - nav.tmpl.html
2023-03-06T17:46:45.283610+00:00 app[web.1]:
2023-03-06T17:46:45.283626+00:00 app[web.1]: [GIN-debug] GET    /static/*filepath         --> github.com/gin-gonic/gin.(*RouterGroup).createStaticHandler.func1 (2 handlers)
2023-03-06T17:46:45.283629+00:00 app[web.1]: [GIN-debug] HEAD   /static/*filepath         --> github.com/gin-gonic/gin.(*RouterGroup).createStaticHandler.func1 (2 handlers)
2023-03-06T17:46:45.283644+00:00 app[web.1]: [GIN-debug] GET    /                         --> main.main.func1 (2 handlers)
2023-03-06T17:46:45.283660+00:00 app[web.1]: [GIN-debug] [WARNING] You trusted all proxies, this is NOT safe. We recommend you to set a value.
2023-03-06T17:46:45.283660+00:00 app[web.1]: Please check https://pkg.go.dev/github.com/gin-gonic/gin#readme-don-t-trust-all-proxies for details.
2023-03-06T17:46:45.283666+00:00 app[web.1]: [GIN-debug] Listening and serving HTTP on :41763
2023-03-06T17:46:45.354966+00:00 heroku[web.1]: State changed from starting to up
2023-03-06T17:46:58.000000+00:00 app[api]: Build succeeded
2023-03-06T17:47:41.010183+00:00 app[web.1]: [GIN] 2023/03/06 - 17:47:41 | 200 |     562.047µs |  204.14.236.211 | GET      "/"
2023-03-06T17:47:41.013474+00:00 heroku[router]: at=info method=GET path="/" host=go-getting-started-update.herokuapp.com request_id=fb0d39df-1e8c-4a29-86d3-8c9b9b256abd fwd="204.14.236.211" dyno=web.1 connect=0ms service=1ms status=200 bytes=6979 protocol=https
2023-03-06T17:47:41.077966+00:00 app[web.1]: [GIN] 2023/03/06 - 17:47:41 | 200 |    9.411982ms |  204.14.236.211 | GET      "/static/main.css"
2023-03-06T17:47:41.081163+00:00 heroku[router]: at=info method=GET path="/static/main.css" host=go-getting-started-update.herokuapp.com request_id=7075befe-37d7-4429-963e-f91e8f25c2be fwd="204.14.236.211" dyno=web.1 connect=0ms service=11ms status=200 bytes=823 protocol=https

Visit your application in the browser again, and you’ll see another log message generated.

Press Control+C to stop streaming the logs.

Define a Procfile

Use a Procfile, a text file in the root directory of your application, to explicitly declare what command should be executed to start your app.

The Procfile in the example app you deployed looks like this:

web: go-getting-started

This declares a single process type, web, and the command needed to run it. The name web is important here. It declares that this process type will be attached to the HTTP routing stack of Heroku, and receive web traffic when deployed. The command used here, go-getting-started is the compiled binary of the getting started app. The heroku build process makes this compiled binary available on the $PATH.

Procfiles can contain additional process types. For example, you might declare one for a background worker process that processes items off of a queue.

Scale the app

Right now, your app is running on a single web dyno. Think of a dyno as a lightweight container that runs the command specified in the Procfile.

You can check how many dynos are running using the ps command:

$ heroku ps
=== web (Eco): `go-getting-started`
web.1: up 2015/05/12 11:28:21 (~ 4m ago)

By default, your app is deployed on an eco dyno. Eco dynos will sleep after a half hour of inactivity (if they don’t receive any traffic). This causes a delay of a few seconds for the first request upon waking. Subsequent requests will perform normally. Eco dynos also consume from a monthly, account-level quota of eco dyno hours - as long as the quota is not exhausted, all eco apps can continue to run.

To avoid dyno sleeping, you can upgrade to a Basic or Professional dyno type as described in the Dyno Types article. For example, if you migrate your app to a professional dyno, you can easily scale it by running a command telling Heroku to execute a specific number of dynos, each running your web process type.

Scaling an application on Heroku is equivalent to changing the number of dynos that are running. Scale the number of web dynos to zero:

$ heroku ps:scale web=0

Access the app again by hitting refresh on the web tab, or heroku open to open it in a web tab. You will get an error message because you no longer have any web dynos available to serve requests.

Scale it up again:

$ heroku ps:scale web=1

Declare app dependencies

Heroku recognizes an app as being written in Go by the existence of a go.mod file in the root directory. The demo app you deployed already has a go.mod file, and it looks something like this:

module github.com/heroku/go-getting-started

// +heroku goVersion go1.20
go 1.20

require (
    github.com/gin-gonic/gin v1.9.0
    github.com/heroku/x v0.0.55
)

require (
    github.com/bytedance/sonic v1.8.0 // indirect
    github.com/chenzhuoyu/base64x v0.0.0-20221115062448-fe3a3abad311 // indirect
    github.com/gin-contrib/sse v0.1.0 // indirect
    github.com/go-playground/locales v0.14.1 // indirect
    github.com/go-playground/universal-translator v0.18.1 // indirect
    github.com/go-playground/validator/v10 v10.11.2 // indirect
    github.com/goccy/go-json v0.10.0 // indirect
    github.com/json-iterator/go v1.1.12 // indirect
    github.com/klauspost/cpuid/v2 v2.0.9 // indirect
    github.com/leodido/go-urn v1.2.1 // indirect
    github.com/mattn/go-isatty v0.0.17 // indirect
    github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421 // indirect
    github.com/modern-go/reflect2 v1.0.2 // indirect
    github.com/pelletier/go-toml/v2 v2.0.6 // indirect
    github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
    github.com/ugorji/go/codec v1.2.9 // indirect
    golang.org/x/arch v0.0.0-20210923205945-b76863e36670 // indirect
    golang.org/x/crypto v0.5.0 // indirect
    golang.org/x/net v0.7.0 // indirect
    golang.org/x/sys v0.5.0 // indirect
    golang.org/x/text v0.7.0 // indirect
    google.golang.org/protobuf v1.28.1 // indirect
    gopkg.in/yaml.v3 v3.0.1 // indirect
)

The go.mod file is used by Go tool and specifies both the dependencies that are required to build your application and the build configuration Heroku should use to compile the application. This Go app has a few dependencies, primarily on Gin, a HTTP web framework.

When an app is deployed, Heroku reads this file, installs an appropriate Go version and compiles your code using go install ..

Run the app locally

Running apps locally in your own dev environment requires a little more effort. Go is a compiled language and you must compile the application and ensure it available on your $PATH, which can be done with one command:

$ go install -v .
github.com/heroku/go-getting-started

Now start your application locally using the heroku local command, which was installed as part of the Heroku CLI:

$ heroku local web --port 5001
[OKAY] Loaded ENV .env File as KEY=VALUE Format
11:58:15 AM web.1 |  [GIN-debug] Listening and serving HTTP on :5001

Just like Heroku, heroku local examines the Procfile to determine what to run.

Open http://localhost:5001 with your web browser. You should see your app running locally.

To stop the app from running locally, go back to your terminal window and press Ctrl+C to exit.

Push local changes

In this step you’ll learn how to propagate a local change to the application through to Heroku. As an example, you’ll modify the application to add an additional dependency and the code to use it.

Dependencies are managed with the Go tool .

Let’s modify the app to use the Blackfriday markdown parser. Since this dependency is not already used by your application we need to tell go to fetch a copy of the dependency:

$ go get github.com/russross/blackfriday@v2
go: downloading github.com/russross/blackfriday v2.0.0+incompatible
go: downloading github.com/shurcooL/sanitized_anchor_name v1.0.0
go: added github.com/russross/blackfriday v2.0.0+incompatible

This does 3 things:

1. Downloads v2 of the Blackfriday module and any of it’s dependencies to the module cache.
2. Records the Blackfriday dependency, and its dependencies in go.mod.
3. Records a cryptographic sum of Blackfriday and it’s dependencies in go.sum

Next, let’s add the new dependency to the vendor folder. This will allow go install to find the dependencies during builds both locally and during remote builds. Vendoring also ensures that builds are repeatable and resistant to erosion.

$ go mod vendor

After that let’s introduce a new route, /mark, which will show the HTML rendered by the parser. Modify main.go so that it uses Blackfriday by adding "github.com/russross/blackfriday" to the list of imports, so it looks something like this:

import (
    "log"
    "net/http"
    "os"

    "github.com/gin-gonic/gin"
    _ "github.com/heroku/x/hmetrics/onload"
    "github.com/russross/blackfriday"
)

Next, modify the main() function to introduce a new route that uses blackfriday. Add the following after the existing router.GET() call:

router.GET("/mark", func(c *gin.Context) {
  c.String(http.StatusOK, string(blackfriday.Run([]byte("**hi!**"))))
})

Finally, let’s recompile and start the program locally to manually test our new endpoint:

$ go install -v .
$ heroku local --port 5001

Visit your application at the new /mark route: http://localhost:5001/mark. You should now see the textual representation of the HTML generated from the Markdown: <p><strong>hi!</strong></p>.

To finish up, let’s deploy the local changes to Heroku. Almost every deploy of a Go application to Heroku follows the same pattern.

First, make sure that any unused modules have been removed from your application:

$ go mod tidy

Next, add any modified or new files to the git repository and commit them:

$ git add -A .
$ git commit -m "Markdown demo dependency"
[blackFriday fc791f7] Markdown demo dependency
 20 files changed, 5962 insertions(+)
 create mode 100644 vendor/github.com/russross/blackfriday/.gitignore
 create mode 100644 vendor/github.com/russross/blackfriday/.travis.yml
 create mode 100644 vendor/github.com/russross/blackfriday/LICENSE.txt
 create mode 100644 vendor/github.com/russross/blackfriday/README.md
 create mode 100644 vendor/github.com/russross/blackfriday/block.go
 create mode 100644 vendor/github.com/russross/blackfriday/doc.go
 create mode 100644 vendor/github.com/russross/blackfriday/esc.go
 create mode 100644 vendor/github.com/russross/blackfriday/html.go
 create mode 100644 vendor/github.com/russross/blackfriday/inline.go
 create mode 100644 vendor/github.com/russross/blackfriday/markdown.go
 create mode 100644 vendor/github.com/russross/blackfriday/node.go
 create mode 100644 vendor/github.com/russross/blackfriday/smartypants.go
 create mode 100644 vendor/github.com/shurcooL/sanitized_anchor_name/.travis.yml
 create mode 100644 vendor/github.com/shurcooL/sanitized_anchor_name/LICENSE
 create mode 100644 vendor/github.com/shurcooL/sanitized_anchor_name/README.md
 create mode 100644 vendor/github.com/shurcooL/sanitized_anchor_name/main.go

Deploy just as you did previously:

$ git push heroku main

And finally, check that your new code is working:

$ heroku open mark

Provision add-ons

Add-ons are third-party cloud services that provide out-of-the-box additional services for your application, from persistence through logging to monitoring and more.

By default, Heroku stores 1500 lines of logs from your application. However, it makes the full log stream available as a service - and several add-on providers have written logging services that provide things such as log persistence, search, and email and SMS alerts.

In this step you will provision one of these logging add-ons, Papertrail.

Provision the papertrail logging add-on:

$ heroku addons:create papertrail
Creating giggling-carefully-3978... done
Adding giggling-carefully-3978 to polar-inlet-4930... done
Setting PAPERTRAIL_API_TOKEN and restarting polar-inlet-4930... done, v5
Welcome to Papertrail. Questions and ideas are welcome (support@papertrailapp.com). Happy logging!

The add-on is now deployed and configured for your application. You can list add-ons for your app like this:

$ heroku addons

To see this particular add-on in action, visit your application’s Heroku URL a few times. Each visit will generate more log messages, which should now get routed to the Papertrail add-on. Visit the Papertrail console to see the log messages:

$ heroku addons:open papertrail

Your browser will open up a Papertrail web console, showing the latest log events. The interface lets you search and set up alerts:

Start a one off dyno

You can run a command, typically scripts and applications that are part of your app, in a one-off dyno using the heroku run command. To get a real feel for how dynos work, let’s create a one-off dyno that runs the bash command, which opens up a shell on that dyno. You can then execute commands there. Each dyno has its own ephemeral filespace, populated with your app and its dependencies - once the command completes (in this case, bash), the dyno is removed:

$ heroku run bash
Running bash on ⬢ go-getting-started... up, run.9087
~ $ ls
Dockerfile  Procfile   app.json  go.mod  heroku.yml  static     vendor
Makefile    README.md  bin       go.sum  main.go     templates
~ $ exit
exit

Don’t forget to type exit to exit the shell and terminate the dyno.

If you receive an error, Error connecting to process, then you may need to configure your firewall.

Define config vars

Heroku lets you externalize configuration, storing data such as encryption keys or external resource addresses in config vars.

At runtime, config vars are exposed as environment variables to the application. Your application is already reading one config var, the $PORT config var. $PORT is automatically set by Heroku on web dynos. Let’s explore how to use user-set config vars in your Go application.

Modify main.go and add a repeatHandler function that returns Hello From Go! the number of times specified by the value of the REPEAT environment variable. Change the file so that it reads like this:

package main

import (
    "bytes"
    "log"
    "net/http"
    "os"
    "strconv"

    "github.com/gin-gonic/gin"
    _ "github.com/heroku/x/hmetrics/onload"
    "github.com/russross/blackfriday"
)

func repeatHandler(r int) gin.HandlerFunc {
    return func(c *gin.Context) {
        var buffer bytes.Buffer
        for i := 0; i < r; i++ {
            buffer.WriteString("Hello from Go!\n")
        }
        c.String(http.StatusOK, buffer.String())
    }
}

func main() {
    port := os.Getenv("PORT")

    if port == "" {
        log.Fatal("$PORT must be set")
    }

    tStr := os.Getenv("REPEAT")
    repeat, err := strconv.Atoi(tStr)
    if err != nil {
        log.Printf("Error converting $REPEAT to an int: %q - Using default\n", err)
        repeat = 5
    }

    router := gin.New()
    router.Use(gin.Logger())
    router.LoadHTMLGlob("templates/*.tmpl.html")
    router.Static("/static", "static")

    router.GET("/", func(c *gin.Context) {
        c.HTML(http.StatusOK, "index.tmpl.html", nil)
    })

    router.GET("/mark", func(c *gin.Context) {
        c.String(http.StatusOK, string(blackfriday.Run([]byte("**hi!**"))))
    })

    router.GET("/repeat", repeatHandler(repeat))

    router.Run(":" + port)
}

heroku local will automatically set up the environment based on the contents of the .env file in your local directory. In the top-level directory of your project there is already a .env file that has the following contents:

REPEAT=10

Recompile the app and run it:

$ go install -v .
$ heroku local

When you access the /repeat route on the app at http://localhost:5001/repeat you’ll see “Hello From Go!” ten times.

To set the config var on Heroku, execute the following:

$ heroku config:set REPEAT=10
Setting config vars and restarting polar-inlet-4930... done, v6
REPEAT: 10

View the config vars that are set using heroku config:

$ heroku config
== polar-inlet-4930 Config Vars
PAPERTRAIL_API_TOKEN: abcfaketoken123
REPEAT:               10

Deploy the changes to heroku using what you learned in the Push local changes section and try it out by visiting the /repeat handler of your application:

$ heroku open repeat

Use a database

The add-on marketplace has a large number of data stores, from Redis and MongoDB providers, to Postgres and MySQL. In this step, you add a Heroku Postgres Essential-0 database to your app.

Add the database:

$ heroku addons:create heroku-postgresql:essential-0
Creating heroku-postgresql:essential-0 on ⬢ go-getting-started... ~$0.007/hour (max $5/month)
Database should be available soon
postgresql-curved-22223 is being created in the background. The app will restart when complete...
Use heroku addons:info postgresql-curved-22223 to check creation progress
Use heroku addons:docs heroku-postgresql to view documentation

This creates a database and sets the $DATABASE_URL environment variable. Listing the config vars for your app will display the value of $DATABASE_URL:

$ heroku config
=== polar-inlet-4930 Config Vars
DATABASE_URL:                postgres://xx:yyy@host:5432/d8slm9t7b5mjnd

Heroku also provides a pg command that shows a lot more:

$ heroku pg
=== DATABASE_URL
Plan:                  Essential 0
Status:                Available
Connections:           0/20
PG Version:            15.5
Created:               2024-05-01 16:00 UTC
Data Size:             8.6 MB/1.00 GB (0.84%) (In compliance)
Tables:                0
Fork/Follow:           Unsupported
Rollback:              Unsupported
Continuous Protection: Off
Add-on:                postgresql-defined-78209

This indicates that you have an essential-0 database, running Postgres 15.5 with no tables.

Let’s add a route to the application that will use this database.

Just like the blackfriday module, we need to go get Go’s postgresql module, github.com/lib/pq, before we can use it.

$ go get github.com/lib/pq@v1
go: finding github.com/lib/pq v1.0.0
go: downloading github.com/lib/pq v1.0.0
go: extracting github.com/lib/pq v1.0.0

And just like before, we add the module to the vendor folder:

$ go mod vendor

Add a dbFunc function to the app and register the /db route:

package main

import (
    "bytes"
    "database/sql"
    "fmt"
    "log"
    "net/http"
    "os"
    "strconv"
    "time"

    "github.com/gin-gonic/gin"
    _ "github.com/heroku/x/hmetrics/onload"
    _ "github.com/lib/pq"
    "github.com/russross/blackfriday"
)

func repeatHandler(r int) gin.HandlerFunc {
    return func(c *gin.Context) {
        var buffer bytes.Buffer
        for i := 0; i < r; i++ {
            buffer.WriteString("Hello from Go!\n")
        }
        c.String(http.StatusOK, buffer.String())
    }
}

func dbFunc(db *sql.DB) gin.HandlerFunc {
    return func(c *gin.Context) {
        if _, err := db.Exec("CREATE TABLE IF NOT EXISTS ticks (tick timestamp)"); err != nil {
            c.String(http.StatusInternalServerError,
                fmt.Sprintf("Error creating database table: %q", err))
            return
        }

        if _, err := db.Exec("INSERT INTO ticks VALUES (now())"); err != nil {
            c.String(http.StatusInternalServerError,
                fmt.Sprintf("Error incrementing tick: %q", err))
            return
        }

        rows, err := db.Query("SELECT tick FROM ticks")
        if err != nil {
            c.String(http.StatusInternalServerError,
                fmt.Sprintf("Error reading ticks: %q", err))
            return
        }

        defer rows.Close()
        for rows.Next() {
            var tick time.Time
            if err := rows.Scan(&tick); err != nil {
                c.String(http.StatusInternalServerError,
                    fmt.Sprintf("Error scanning ticks: %q", err))
                return
            }
            c.String(http.StatusOK, fmt.Sprintf("Read from DB: %s\n", tick.String()))
        }
    }
}

func main() {
    port := os.Getenv("PORT")

    if port == "" {
        log.Fatal("$PORT must be set")
    }

    tStr := os.Getenv("REPEAT")
    repeat, err := strconv.Atoi(tStr)
    if err != nil {
        log.Printf("Error converting $REPEAT to an int: %q - Using default\n", err)
        repeat = 5
    }

    db, err := sql.Open("postgres", os.Getenv("DATABASE_URL"))
    if err != nil {
        log.Fatalf("Error opening database: %q", err)
    }

    router := gin.New()
    router.Use(gin.Logger())
    router.LoadHTMLGlob("templates/*.tmpl.html")
    router.Static("/static", "static")

    router.GET("/", func(c *gin.Context) {
        c.HTML(http.StatusOK, "index.tmpl.html", nil)
    })

    router.GET("/mark", func(c *gin.Context) {
        c.String(http.StatusOK, string(blackfriday.Run([]byte("**hi!**"))))
    })

    router.GET("/repeat", repeatHandler(repeat))

    router.GET("/db", dbFunc(db))

    router.Run(":" + port)
}

Update your dependencies, commit the new code, and deploy your changes to Heroku:

$ go mod tidy
$ git add -A .
$ git commit -m "/db"
$ git push heroku main
$ heroku open db

Reload the page a few times and, you will see something like this:

Read from DB: 2023-03-06 20:17:29.664738 +0000 +0000
Read from DB: 2023-03-06 20:17:29.820189 +0000 +0000
Read from DB: 2023-03-06 20:17:30.009628 +0000 +0000
Read from DB: 2023-03-06 20:17:30.226158 +0000 +0000
Read from DB: 2023-03-06 20:17:30.464666 +0000 +0000
Read from DB: 2023-03-06 20:17:30.63997 +0000 +0000
Read from DB: 2023-03-06 20:17:30.858864 +0000 +0000

If you have Postgres installed locally, you can use the heroku pg:psql command to connect to the remote database and see all the rows:

$ heroku pg:psql
--> Connecting to postgresql-defined-78209
psql (14.7 (Homebrew))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

go-getting-started-update::DATABASE=> SELECT * FROM ticks;
            tick
----------------------------
 2023-03-06 20:17:11.998688
 2023-03-06 20:17:12.964102
 2023-03-06 20:17:27.640823
 2023-03-06 20:17:28.796569
 2023-03-06 20:17:29.115884
 2023-03-06 20:17:29.314284
 2023-03-06 20:17:29.487526
...

Read more about Heroku PostgreSQL.

A similar technique can be used to install MongoDB or Redis add-ons.

Next steps

You now know how to deploy a Go application, change its configuration, view logs, scale, and attach and use add-ons.

Here’s some recommended reading:

• Read How Heroku Works for a technical overview of the concepts you’ll encounter while writing, configuring, deploying and running applications.
• Visit the Go category to learn more about developing and deploying Go applications.