Makefile: build promtail with CGO_ENABLED if GOHOSTOS=GOOS=linux

[rfratto]

No description provided.

[cyriltovena]

LGTM

[rfratto]

I want to hold off on this a bit for #762 since I know there will be merge conflicts

[sh0rez]

Update: see below

Can you please check the Docker container? It fails for me with

standard_init_linux.go:207: exec user process caused "no such file or directory"

Altough the /usr/local/bin/promtail is in place, it cannot be executed by hand:

/usr/bin # stat promtail
  File: promtail
  Size: 59509104        Blocks: 116232     IO Block: 4096   regular file
Device: beh/190d        Inode: 2032        Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-07-31 08:41:02.000000000
Modify: 2019-07-31 08:36:25.000000000
Change: 2019-07-31 08:36:30.000000000

/usr/bin # ./promtail
sh: ./promtail: not found

Other info:

/usr/bin # file promtail
promtail: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, Go BuildID=_sO-pfbrRk_qJH8MhCzo/Pwigi6dJO36ey-UilkK4/POa4moLK7qN8unm6QH_M/Yeujh4VTwFz48MW6LDnT, BuildID[sha1]=e87eb02001377e33f9c8ca263a0f13825e219549, stripped
/usr/bin # ldd promtail
        /lib64/ld-linux-x86-64.so.2 (0x7fc4c96d8000)
        libdl.so.2 => /lib64/ld-linux-x86-64.so.2 (0x7fc4c96d8000)
        libpthread.so.0 => /lib64/ld-linux-x86-64.so.2 (0x7fc4c96d8000)
        libc.so.6 => /lib64/ld-linux-x86-64.so.2 (0x7fc4c96d8000)

[sh0rez]

Okay, solved it myself. So long story short:

1. The build image is debian. Debian uses glibc.
2. The final container is alpine. Alpine uses muslc.
3. You made the binary dynamic. This means it is dynamic against glibc.
4. Alpine cannot execute glibc stuff
5. Add libc6-compat, then it can

diff --git a/cmd/promtail/Dockerfile b/cmd/promtail/Dockerfile
index a038009..eb0f15e 100644
--- a/cmd/promtail/Dockerfile
+++ b/cmd/promtail/Dockerfile
@@ -9,7 +9,7 @@ WORKDIR /go/src/github.com/grafana/loki
 RUN make clean && make promtail

 FROM       alpine:3.9
-RUN        apk add --update --no-cache ca-certificates tzdata
+RUN        apk add --update --no-cache ca-certificates tzdata libc6-compat
 COPY       --from=build /go/src/github.com/grafana/loki/cmd/promtail/promtail /usr/bin/promtail
 COPY       cmd/promtail/promtail-local-config.yaml /etc/promtail/local-config.yaml
 COPY       cmd/promtail/promtail-docker-config.yaml /etc/promtail/docker-config.yaml

[rfratto]

@sh0rez thanks for investigating!