Deploying a golang app on heroku, build succeed but application error

My golang app runs on port 9000 at my localhost. After deploying it at heroku using godep support, i was able to push and deploy at heroku. However when i try to access the endpoint e.g '/', it shows Application Error. You can see below my code and log while deploying at heroku

package main

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

    "github.com/gorilla/mux"
    "github.com/gorilla/context"

    "gopkg.in/paytm/grace.v1"

    // utilhttp "bitbucket.org/michaelchandrag/chit/pkg/util/http"
    // util "bitbucket.org/michalechandrag/chit/pkg/util"
)

func main() {
    log.Println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$")
    log.Println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$")

    muxRouter := mux.NewRouter()

    muxRouter.HandleFunc("/", Articles)
    http.Handle("/", muxRouter)

    // err = grace.Serve(":"+cfg.Server.Port, context.ClearHandler(http.DefaultServeMux))
    err := grace.Serve(":9000", context.ClearHandler(http.DefaultServeMux))
    if err != nil {
        log.Println("[ERROR GRACEFUL]", err)
        os.Exit(1)
    }

    os.Exit(0)
}

func Articles(w http.ResponseWriter, r *http.Request) {
    // vars := mux.Vars(r)
    w.WriteHeader(http.StatusOK)
    fmt.Fprintf(w, "Hello")
    // r.Close = true
    // w.Header().Set("Content-Type", "application/json")
    // w.Header().Set("Access-Control-Allow-Origin", "*")

    /*if r.Method == "OPTIONS" {
        w.WriteHeader(http.StatusOK)
        return
    }

    if err := fn(w, r); err != nil {
        log.Println(err)
        apiObject := ConstructAPIError(http.StatusInternalServerError, ErrGeneral, SysMsgErrGeneral, MsgErrGeneral)
        SendAPIObject(w, apiObject)
        return
    }*/
}

heroku logs while deploying

-----> Go app detected
-----> Fetching jq... done
-----> Fetching stdlib.sh.v8... done
-----> Checking Godeps/Godeps.json file.
-----> New Go Version, clearing old cache
-----> Installing go1.12.6
-----> Fetching go1.12.6.linux-amd64.tar.gz... done
-----> Running: go install -v -tags heroku ./... 
bitbucket.org/michaelchandrag/chit/pkg
bitbucket.org/michaelchandrag/chit/vendor/github.com/gorilla/context
bitbucket.org/michaelchandrag/chit/vendor/github.com/gorilla/mux
bitbucket.org/michaelchandrag/chit/vendor/gopkg.in/tylerb/graceful.v1
bitbucket.org/michaelchandrag/chit/vendor/gopkg.in/paytm/grace.v1
bitbucket.org/michaelchandrag/chit/pkg/util
bitbucket.org/michaelchandrag/chit

       Installed the following binaries:
            ./bin/chit
-----> Discovering process types
       Procfile declares types -> web
-----> Compressing...
       Done: 7.5M
-----> Launching...
       Released v3
       https://michaelchandrag-project.herokuapp.com/ deployed to Heroku

app logs before and after access endpoint

2:47.954106+00:00 heroku[web.1]: Starting process with command `chit`
2019-07-08T05:02:49.413453+00:00 app[web.1]: 2019/07/08 05:02:49 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T05:02:49.413476+00:00 app[web.1]: 2019/07/08 05:02:49 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T05:02:49.413647+00:00 app[web.1]: 2019/07/08 05:02:49 starting serve on  :9000
2019-07-08T05:03:48.131507+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
2019-07-08T05:03:48.131595+00:00 heroku[web.1]: Stopping process with SIGKILL
2019-07-08T05:03:48.214979+00:00 heroku[web.1]: State changed from starting to crashed
2019-07-08T05:03:48.193205+00:00 heroku[web.1]: Process exited with status 137
2019-07-08T10:38:59.721224+00:00 heroku[web.1]: State changed from crashed to starting
2019-07-08T10:39:00.359017+00:00 heroku[web.1]: Starting process with command `chit`
2019-07-08T10:39:02.232435+00:00 app[web.1]: 2019/07/08 10:39:02 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T10:39:02.232458+00:00 app[web.1]: 2019/07/08 10:39:02 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T10:39:02.232583+00:00 app[web.1]: 2019/07/08 10:39:02 starting serve on  :9000
2019-07-08T10:40:00.462841+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
2019-07-08T10:40:00.462974+00:00 heroku[web.1]: Stopping process with SIGKILL
2019-07-08T10:40:00.555959+00:00 heroku[web.1]: Process exited with status 137
2019-07-08T10:40:00.573427+00:00 heroku[web.1]: State changed from starting to crashed
2019-07-08T13:33:25.021835+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=michaelchandrag-project.herokuapp.com request_id=e6b5c93a-7177-4080-9858-ed925a20c513 fwd="36.74.35.162" dyno= connect= service= status=503 bytes= protocol=https
2019-07-08T13:33:25.566036+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=michaelchandrag-project.herokuapp.com request_id=35c741a9-be4d-48f6-ba99-ba24ddc58b9b fwd="36.74.35.162" dyno= connect= service= status=503 bytes= protocol=https
2019-07-08T13:48:38.294082+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=michaelchandrag-project.herokuapp.com request_id=57a3a243-58f4-4efe-b478-eb660d84fe1f fwd="36.74.35.162" dyno= connect= service= status=503 bytes= protocol=https
2019-07-08T13:48:38.616077+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=michaelchandrag-project.herokuapp.com request_id=0687b8a8-86ae-4c49-a37f-9cbf9e0f75de fwd="36.74.35.162" dyno= connect= service= status=503 bytes= protocol=https

Solution

Your app starts but is getting killed because you don't bind your webserver to the specified port. This is clear from the log message:

2019-07-08T05:03:48.131507+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch

On Heroku you have to bind your HTTP server to the port specified by the PORT environment variable. Your app will be publicly available on default HTTP and HTTPS ports with the help of Heroku gateways.

So start your server on the expected port. Instead of this:

err := grace.Serve(":9000", context.ClearHandler(http.DefaultServeMux))

Do this:

port := os.Getenv("PORT")
if port == "" {
    port = "9000" // Default port if not specified
}
err := grace.Serve(":" + port, context.ClearHandler(http.DefaultServeMux))