Docker throwing "{binary} not found" error - docker

Question

I have a very simple Go app that I'm trying to Dockerize.
package main
import (
"fmt"
"net/http"
"time"
)
func main() {
http.HandleFunc("/", date)
http.HandleFunc("/health", healthCheck)
http.ListenAndServe(":8080", nil)
}
func healthCheck(w http.ResponseWriter, r *http.Request){
fmt.Fprintf(w, "I'm alive!")
}
func date(w http.ResponseWriter, r *http.Request) {
now := time.Now()
fmt.Fprintf(w, now.Format("2006-01-02 15:04:05"))
}
My Dockerfile:
FROM golang:1.14.6
RUN mkdir /app
COPY date.go /app
WORKDIR /app
RUN go build date.go
RUN groupadd -g 999 appuser && \
useradd -r -u 999 -g appuser appuser
USER appuser
EXPOSE 8080
CMD ['/app/date']
However, when I use docker run to run the app, I get the following error:
/bin/sh: 1: [/app/date]: not found
I've commented out the CMD ['/app/date'] line and rebuilt the image, and then was able to exec into it by running
docker run -dit goapp
docker exec -ti [containerid] /bin/bash
This takes me into the /app folder where I do see the date file. And I am able to run /app/date without any issues. I'm not sure what I'm doing wrong.

Answer 1

The CMD is interpreted as JSON, so you need to change the single quotes to double quotes.
CMD ["/app/date"]
This is specified in the Dockerfile documentation:
The exec form is parsed as a JSON array, which means that you must use double-quotes (") around words not single-quotes (').