Execing docker image entrypoint, which is a compiled go app, fails with "not found"

Question

I have built a small Go app and done local testing of it on my Linux VM.

I'm now trying to build a prototype Docker image for it and test running the image. The Dockerfile structure is pretty simple. I base it on Alpine, copy the executable to the root directory and my entrypoint is running the executable.

It fails with "not found".

Now for more details.

Here is the Dockerfile, with some information elided:

FROM <registry>/<namespace>/alpine-base:3.12.3

COPY target/dist/linux-amd64/<appname> /
EXPOSE 8080

RUN echo hello
RUN ls -ltd .
RUN ls -lt
RUN whoami
#ENTRYPOINT ["./<appname>"]
ENTRYPOINT ./<appname>

This is approximately what I do when I build the image:

chmod 777 target/dist/linux-amd64/<appname>
docker build --no-cache -f Dockerfile -t <registry>/<namespace>/<appname>:dev-latest .

This is the output of that:

Sending build context to Docker daemon  14.48MB
Step 1/8 : FROM <registry>/<namespace>/alpine-base:3.12.3
 ---> d7eec24f3d29
Step 2/8 : COPY target/dist/linux-amd64/<appname> /
 ---> e056bbe44bd6
Step 3/8 : EXPOSE 8080
 ---> Running in 921cc1fe8804
Removing intermediate container 921cc1fe8804
 ---> 00b30c5a2770
Step 4/8 : RUN echo hello
 ---> Running in 9fb08d924d3c
hello
Removing intermediate container 9fb08d924d3c
 ---> 6788feafae4b
Step 5/8 : RUN ls -ltd .
 ---> Running in 78e6d4aea09f
drwxr-xr-x    1 root     root          4096 Jan 10 23:02 .
Removing intermediate container 78e6d4aea09f
 ---> 711f3d247efe
Step 6/8 : RUN ls -lt
 ---> Running in 32e703a9d480
total 14200
drwxr-xr-x    5 root     root           340 Jan 10 23:02 dev
drwxr-xr-x    1 root     root          4096 Jan 10 23:02 etc
dr-xr-xr-x  324 root     root             0 Jan 10 23:02 proc
dr-xr-xr-x   13 root     root             0 Jan 10 23:02 sys
-rwxrwxrwx    1 root     root      14480384 Jan 10 22:39 <appname>
drwxr-xr-x    1 root     root          4096 Jan 12  2021 home
drwxr-xr-x    1 root     root          4096 Jan 12  2021 opt
drwxr-xr-x    2 root     root          4096 Dec 16  2020 bin
drwxr-xr-x    2 root     root          4096 Dec 16  2020 sbin
drwxr-xr-x    1 root     root          4096 Dec 16  2020 lib
drwxr-xr-x    5 root     root          4096 Dec 16  2020 media
drwxr-xr-x    2 root     root          4096 Dec 16  2020 mnt
drwx------    2 root     root          4096 Dec 16  2020 root
drwxr-xr-x    2 root     root          4096 Dec 16  2020 run
drwxr-xr-x    2 root     root          4096 Dec 16  2020 srv
drwxrwxrwt    2 root     root          4096 Dec 16  2020 tmp
drwxr-xr-x    1 root     root          4096 Dec 16  2020 usr
drwxr-xr-x    1 root     root          4096 Dec 16  2020 var
Removing intermediate container 32e703a9d480
 ---> 68871e80b517
Step 7/8 : RUN whoami
 ---> Running in 40b2460bc349
kube
Removing intermediate container 40b2460bc349
 ---> 4cf57c0b5f10
Step 8/8 : ENTRYPOINT ./<appname>
 ---> Running in 3c57717800ab
Removing intermediate container 3c57717800ab
 ---> eaafc953da46
Successfully built eaafc953da46
Successfully tagged <registry>/<namespace>/<appname>:dev-latest

And this is what I run to test it:

docker rm <appname>-1
docker run -P --name=<appname>-1 -d -t <registry>/<namespace>/<appname>:dev-latest
docker logs <appname>-1

And this is the output:

docker rm <appname>-1
<appname>-1
docker run -P --name=<appname>-1 -d -t <registry>/<namespace>/<appname>:dev-latest
66bb4756783b3ef64d9a4b0d8b7227184ba3b5a3fde25ea0d19b9523285d76b7
docker logs <appname>-1
/bin/sh: ./<appname>: not found

It says "not found". I don't understand that. I showed the contents of the root directory. The file is clearly there. Is this error saying that some OTHER file is not found, like if it thought it was a shell script and the shebang pointed to a shell that doesn't exist?

Update:

So the one tiny little detail that I realized I didn't mention in the original post is that disabling CGO is not going to be possible. The entire reason for this app is to link with a C library and call functions in it, so I have to use Cgo.

What I conclude from these helpful comments and other threads like Go-compiled binary won't run in an alpine docker container on Ubuntu host , is that my "workaround" of changing to an ubuntu base image is actually the only reasonable solution.

It seems like this output is comming from your program. If the file cant be found you would see something like this. `docker: Error response from daemon: OCI runtime create failed: container_linux.go:380: starting container process caused: exec: "./foo": stat ./foo: no such file or directory: unknown.` — The Fool, Jan 10 '22 at 23:24
Maybe due to the way you build the app. Did you try static linking? — The Fool, Jan 10 '22 at 23:26
That can also happen if the image is missing a shared-library dependency of the binary; have you tried `docker run --rm --entrypoint ldd your-image ./appname`? (Consider changing `ENTRYPOINT` to `CMD` to make this kind of diagnostic easier.) — David Maze, Jan 10 '22 at 23:34
Congruent with David Maze and The Fool, I'll guess you built that binary with CGO on a glibc based system, so you can't run it in musl-based system like alpine. — erik258, Jan 10 '22 at 23:35
Ok. It is definitely dynamically linked. That surprised me. I guess cgo doesn't static link by default. I'm not sure I can even make it do that. I'll either figure out how to make it static link, or I'll push the shared libraries into the image. — David M. Karr, Jan 11 '22 at 00:15
I think I've now done everything that should be required to make it work if it's dynamically linked, and it still gives the same error, so I think your other comment about glibc vs. musl (never heard of that) is relevant. Can I cross-compile to something that will work on Alpine? — David M. Karr, Jan 11 '22 at 00:28

serge-v · Answer 1 · 2022-01-15T02:24:55.417

-1

If disabling cgo is not an option you can pass "-static" parameter to the linker. Example:

package main

/*
#include <stdio.h>

void test_puts() {
        puts("puts() called");
}
*/
import "C"

func main() {
        C.test_puts()
}

Run:

go build --ldflags '-extldflags "-static"'

edited Jan 15 '22 at 02:24

answered Jan 11 '22 at 22:28

serge-v

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Execing docker image entrypoint, which is a compiled go app, fails with "not found"

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