I had a docker file that was working fine. However to remote debug it , I read that I needed to install dlv on it and then I need to run dlv and pass the parameter of the app I am trying to debug. So after installing dlv on it and attempting to run it. I get the error
exec /dlv: no such file or directory
This is the docker file
FROM golang:1.18-alpine AS builder
# Build Delve for debugging
RUN go install github.com/go-delve/delve/cmd/dlv@latest
# Create and change to the app directory.
WORKDIR /app
ENV CGO_ENABLED=0
# Retrieve application dependencies.
COPY go.* ./
RUN go mod download
# Copy local code to the container image.
COPY . ./
# Build the binary.
RUN go build -gcflags="all=-N -l" -o fooapp
# Use the official Debian slim image for a lean production container.
FROM debian:buster-slim
EXPOSE 8000 40000
RUN set -x && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
ca-certificates && \
rm -rf /var/lib/apt/lists/*
# Copy the binary to the production image from the builder stage.
#COPY --from=builder /app/fooapp /app/fooapp #commented this out
COPY --from=builder /go/bin/dlv /dlv
# Run dlv as pass fooapp as parameter
CMD ["/dlv", "--listen=:40000", "--headless=true", "--api-version=2", "--accept-multiclient", "exec", "/app/fooapp"]
The above results in exec /dlv: no such file or directory
I am not sure why this is happening. Being new to docker , I have tried different ways to debug it. I tried using dive to check and see if the image has dlv on it in the path /dlv and it does. I have also attached an image of it
CodePudding user response：
TL;DR
Run apt-get install musl, then /dlv should work as expected.
Explanation
Follow these steps:
docker run -it <image-name> shapt-get install filefile /dlv
Then you can see the following output:
/dlv: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-x86_64.so.1, Go BuildID=xV8RHgfpp-zlDlpElKQb/DOLzpvO_A6CJb7sj1Nxf/aCHlNjW4ruS1RXQUbuCC/JgrF83mgm55ntjRnBpHH, not stripped
The confusing no such file or directory (see this question for related discussions) is caused by the missing /lib/ld-musl-x86_64.so.1.
As a result, the solution is to install the musl library by following its documentation.
My answer is inspired by this answer.
CodePudding user response：
You built dlv in alpine-based distro. dlv executable is linked against libc.musl:
# ldd dlv
linux-vdso.so.1 (0x00007ffcd251d000)
libc.musl-x86_64.so.1 => not found
But then you switched to glibc-based image debian:buster-slim. That image doesn't have the required libraries.
# find / -name libc.musl*
<nothing found>
That's why you can't execute dlv - the dynamic linker fails to find the proper lib.
You need to build in glibc-based docker. For example, replace the first line
FROM golang:bullseye AS builder
BTW. After you build you need to run the container in the priviledged mode
$ docker build . -t try-dlv
...
$ docker run --privileged --rm try-dlv
API server listening at: [::]:40000
2022-10-30T10:51:02Z warning layer=rpc Listening for remote connections (connections are not authenticated nor encrypted)
In non-priviledged container dlv is not allowed to spawn a child process.
$ docker run --rm try-dlv
API server listening at: [::]:40000
2022-10-30T10:55:46Z warning layer=rpc Listening for remote connections (connections are not authenticated nor encrypted)
could not launch process: fork/exec /app/fooapp: operation not permitted
Really Minimal Image
You use debian:buster-slim to minimize the image, it's size is 80 MB. But if you need a really small image, use busybox, it is only 4.86 MB overhead.
FROM golang:bullseye AS builder
# Build Delve for debugging
RUN go install github.com/go-delve/delve/cmd/dlv@latest
# Create and change to the app directory.
WORKDIR /app
ENV CGO_ENABLED=0
# Retrieve application dependencies.
COPY go.* ./
RUN go mod download
# Copy local code to the container image.
COPY . ./
# Build the binary.
RUN go build -o fooapp .
# Download certificates
RUN set -x && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
ca-certificates
# Use the official Debian slim image for a lean production container.
FROM busybox:glibc
EXPOSE 8000 40000
# Copy the binary to the production image from the builder stage.
COPY --from=builder /app/fooapp /app/fooapp
# COPY --from=builder /app/ /app
COPY --from=builder /go/bin/dlv /dlv
COPY --from=builder /etc/ssl /etc/ssl
# Run dlv as pass fooapp as parameter
CMD ["/dlv", "--listen=:40000", "--headless=true", "--api-version=2", "--accept-multiclient", "exec", "/app/fooapp"]
# ENTRYPOINT ["/bin/sh"]
The image size is 25 MB, of which 18 MB are from dlv and 2 MB are from Hello World application.
While choosing the images care should be taken to have the same flavors of libc. golang:bullseye links against glibc. Hence, the minimal image must be glibc-based.
But if you want a bit more comfort, use alpine with gcompat package installed. It is a reasonably rich linux with lots of external packages for just extra 6 MB compared to busybox.
FROM golang:bullseye AS builder
# Build Delve for debugging
RUN go install github.com/go-delve/delve/cmd/dlv@latest
# Create and change to the app directory.
WORKDIR /app
ENV CGO_ENABLED=0
# Copy local code to the container image.
COPY . ./
# Retrieve application dependencies.
RUN go mod tidy
# Build the binary.
RUN go build -o fooapp .
# Use alpine lean production container.
# FROM busybox:glibc
FROM alpine:latest
# gcompat is the package to glibc-based apps
# ca-certificates contains trusted TLS CA certs
# bash is just for the comfort, I hate /bin/sh
RUN apk add gcompat ca-certificates bash
EXPOSE 8000 40000
# Copy the binary to the production image from the builder stage.
COPY --from=builder /app/fooapp /app/fooapp
# COPY --from=builder /app/ /app
COPY --from=builder /go/bin/dlv /dlv
# Run dlv as pass fooapp as parameter
CMD ["/dlv", "--listen=:40000", "--headless=true", "--api-version=2", "--accept-multiclient", "exec", "/app/fooapp"]
# ENTRYPOINT ["/bin/bash"]