Running a go script wtih cron in Docker - docker

Question

I've been trying to run a go script with cron under Ubuntu 16.04 Docker image. Here are the files that I've
Dockerfile
FROM couchbase
RUN apt-get update
RUN apt-get install gcc make -y
RUN apt-get install golang-1.10 git -y
ADD src/crontab.txt /crontab.txt
ADD src/backup.sh /backup.sh
ADD src/backup.go /backup.go
ADD src/file.txt /file.txt
COPY entry.sh /entry.sh
RUN chmod 755 /backup.sh /entry.sh
RUN /usr/bin/crontab /crontab.txt
RUN apt-get install vim -y
CMD ["/entry.sh"]
entry.sh
#!/bin/sh
/usr/sbin/cron -f -l 8
src/crontab.txt
* * * * * /backup.sh >> /var/log/backup.log
src/backup.sh
#!/bin/sh
chmod 666 /var/log/backup.log
/usr/lib/go-1.10/bin/go run backup.go
backup.go
package main
import (
"log"
"os"
"strings"
)
func init() {
file, err := os.OpenFile("/var/log/backup.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0666)
if err != nil {
log.Fatal(err)
}
log.SetOutput(file)
}
func main() {
log.Println("Writing log")
}
I checked and the cron task is running each minute. The go installation is there in the folder and when I exec into the container it works, but the backup.go script is not logging anything. When I trigger the script manually it works though. The container that I'm using has Ubuntu 16.04 and I want it cause I don't have to do a couchbase installation.

Answer 1

You can do this simpler by using a multi stage build. First use a Go image to compile a standalone executable from your src/backup.go. Then switch to a coughbase image and copy the executable from the previous step.
Dockerfile:
# use a first-stage image to build the go code
# we'll change it later
FROM golang:1.10 AS build
# for now we only need the go code
COPY src/backup.go backup.go
# build a standalone executable
RUN go build -o /backup backup.go
# switch to a second-stage production image
FROM couchbase
# setup cronjob
COPY src/crontab.txt /crontab.txt
RUN /usr/bin/crontab /crontab.txt
# copy the executable from the first stage
# into the production image
COPY --from=build /backup /backup
CMD ["/usr/sbin/cron", "-f", "-l", "8"]
src/crontab.txt:
* * * * * /backup >> /var/log/backup.log
Build and run like this:
docker build . -t backup
# start in backgroud
docker run --name backup -d test
# check if it works
docker exec backup tail -f /var/log/backup.log
On the next minute :
2021/04/09 19:05:01 Writing log