Use ENTRYPOINT exec form instead of shell form

[futek]

The image has no shell at /bin/sh so the ENTRYPOINT shell form does not work:

$ docker run --rm itzg/rcon-cli:1.4.7 --help
Unable to find image 'itzg/rcon-cli:1.4.7' locally
1.4.7: Pulling from itzg/rcon-cli
8839a1e05eed: Pull complete
Digest: sha256:8470c29d26d7abc1475d2adc4b5e5a6f746a788763f511757bf179c39e3f26c9
Status: Downloaded newer image for itzg/rcon-cli:1.4.7
docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"/bin/sh\": stat /bin/sh: no such file or directory": unknown.

$ GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -o rcon-cli .
$ docker build -t rcon-cli .
Sending build context to Docker daemon   12.2MB
Step 1/3 : FROM scratch
 --->
Step 2/3 : COPY rcon-cli /
 ---> 0dd2badd83fe
Step 3/3 : ENTRYPOINT /rcon-cli
 ---> Running in d81dcc3f9b4c
Removing intermediate container d81dcc3f9b4c
 ---> 327b6d337275
Successfully built 327b6d337275
Successfully tagged rcon-cli:latest
$ docker run --rm rcon-cli --help
docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"/bin/sh\": stat /bin/sh: no such file or directory": unknown.

You can work around it by overriding the ENTRYPOINT of the image:

$ docker run --rm --entrypoint /rcon-cli itzg/rcon-cli:1.4.7 --help

rcon-cli is a CLI for attaching to an RCON enabled game server, such as Minecraft.
Without any additional arguments, the CLI will start an interactive session with
the RCON server.

...

Using the ENTRYPOINT exec form instead (i.e. ENTRYPOINT ["/rcon-cli"]) makes it work out of the box:

$ GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -o rcon-cli .
$ docker build -t rcon-cli .
Sending build context to Docker daemon   12.2MB
Step 1/3 : FROM scratch
 --->
Step 2/3 : COPY rcon-cli /
 ---> Using cache
 ---> 0dd2badd83fe
Step 3/3 : ENTRYPOINT [ "/rcon-cli" ]
 ---> Running in a96eb138ebf7
Removing intermediate container a96eb138ebf7
 ---> d649b44a2dca
Successfully built d649b44a2dca
Successfully tagged rcon-cli:latest
$ docker run --rm rcon-cli --help

rcon-cli is a CLI for attaching to an RCON enabled game server, such as Minecraft.
Without any additional arguments, the CLI will start an interactive session with
the RCON server.

...

[itzg]

Well, that's embarrassing. I defined the docker build but apparently never tested the image. Thanks for fixing this!

[itzg]

Latest image (at 1.4.8) includes your fix