docker unable to resolve DNS when building container

I'm so confused by this, I'm trying to build a docker image for m4b-tools, and I've followed all the instructions. Halfway through the install process, it decided it can't resolve github.com. This is after installing numerous other packages. And when I attempt to ping from busybox, that works fine, to the same domain too. I went into the Dockerfile, pulled out the commands and ran them perfectly from the command line. So the host can resolve fine, Docker itself can resolve fine, and presumably there's nothing wrong with the build, since I can't see the same issue online.

I don't know why this becomes an issue at this point. It's not an issue with DNS on the host, or within Docker when rying to ping, only when using wget to build this image.

I'm attempting to run this on the latest version of Ubuntu which I just installed today along with Docker using WSL2.

Here's the log output where it fails:

#8 33.10 Connecting to github.com (github.com)|140.82.121.4|:443... connected.
#8 33.16 HTTP request sent, awaiting response... 302 Found
#8 33.42 Location: https://codeload.github.com/sandreas/mp4v2/zip/master [following]
#8 33.42 --2021-08-23 16:39:14--  https://codeload.github.com/sandreas/mp4v2/zip/master
#8 33.42 Resolving codeload.github.com (codeload.github.com)... failed: Try again.
#8 38.43 wget: unable to resolve host address 'codeload.github.com'
------

And here's the Dockerfile:

    ##############################
#
#   m4b-tool build image
#   alias m4b-tool='docker run -it --rm -u $(id -u):$(id -g) -v "$(pwd)":/mnt m4b-tool'
#   alias m4b-tool='docker run -it --entrypoint=m4b-tool-pre --rm -u $(id -u):$(id -g) -v "$(pwd)":/mnt m4b-tool'
##############################
FROM alpine:3.14 as builder

ARG FDK_AAC_VERSION=2.0.1
ARG FDK_AAC_URL="https://github.com/mstorsjo/fdk-aac/archive/v$FDK_AAC_VERSION.tar.gz"
ARG FDK_AAC_SHA256=a4142815d8d52d0e798212a5adea54ecf42bcd4eec8092b37a8cb615ace91dc6

RUN echo "---- INSTALL BUILD DEPENDENCIES ----" \
    && apk add --no-cache --update --upgrade --virtual=build-dependencies \
    autoconf \
    libtool \
    automake \
    boost-dev \
    build-base \
    gcc \
    git \
    tar \
    wget \
&& echo "---- COMPILE SANDREAS MP4V2 (for sort-title, sort-album and sort-author) ----" \
  && cd /tmp/ \
  && wget https://github.com/sandreas/mp4v2/archive/master.zip \
  && unzip master.zip \
  && cd mp4v2-master \
  && ./configure && \
  make -j4 && \
  make install && make distclean \
&& echo "---- PREPARE FDKAAC-DEPENDENCIES ----" \
  && cd /tmp/ \
  && wget -O fdk-aac.tar.gz "$FDK_AAC_URL" \
  && tar xfz fdk-aac.tar.gz \
  && cd fdk-aac-* && ./autogen.sh && ./configure --enable-static --disable-shared && make -j$(nproc) install \
&& echo "---- COMPILE FDKAAC ENCODER (executable binary for usage of --audio-profile) ----" \
    && cd /tmp/ \
    && wget https://github.com/nu774/fdkaac/archive/1.0.0.tar.gz \
    && tar xzf 1.0.0.tar.gz \
    && cd fdkaac-1.0.0 \
    && autoreconf -i && ./configure --enable-static --disable-shared && make -j4 && make install && rm -rf /tmp/* \
&& echo "---- REMOVE BUILD DEPENDENCIES (to keep image small) ----" \
    && apk del --purge build-dependencies && rm -rf /tmp/*

##############################
#
#   m4b-tool development image
#
##############################
FROM alpine:3.14
ENV WORKDIR /mnt/
ENV M4BTOOL_TMP_DIR /tmp/m4b-tool/


RUN echo "---- INSTALL RUNTIME PACKAGES ----" && \
  apk add --no-cache --update --upgrade \
  # mp4v2: required libraries
  libstdc++ \
  # m4b-tool: php cli, required extensions and php settings
  php7-cli \
  php7-dom \
  php7-json \
  php7-xml \
  php7-mbstring \
  php7-phar \
  php7-tokenizer \
  php7-xmlwriter \
  php7-openssl \
  && echo "date.timezone = UTC" >> /etc/php7/php.ini



# copy ffmpeg static with libfdk from mwader docker image
COPY --from=mwader/static-ffmpeg:4.4.0 /ffmpeg /usr/local/bin/

# copy compiled mp4v2 binaries, libs and fdkaac encoder to runtime image
COPY --from=builder /usr/local/bin/mp4* /usr/local/bin/fdkaac /usr/local/bin/
COPY --from=builder /usr/local/lib/libmp4v2* /usr/local/lib/


ARG M4B_TOOL_DOWNLOAD_LINK="https://github.com/sandreas/m4b-tool/releases/latest/download/m4b-tool.tar.gz"

# workaround to copy a local m4b-tool.phar IF it exists
ADD ./Dockerfile ./dist/m4b-tool.phar* /tmp/
RUN echo "---- INSTALL M4B-TOOL ----" \
    && if [ ! -f /tmp/m4b-tool.phar ]; then \
            wget "${M4B_TOOL_DOWNLOAD_LINK}" -O /tmp/m4b-tool.tar.gz && \
            if [ ! -f /tmp/m4b-tool.phar ]; then \
                tar xzf /tmp/m4b-tool.tar.gz -C /tmp/ && rm /tmp/m4b-tool.tar.gz ;\
            fi \
       fi \
    && mv /tmp/m4b-tool.phar /usr/local/bin/m4b-tool \
    && M4B_TOOL_PRE_RELEASE_LINK=$(wget -q -O - https://github.com/sandreas/m4b-tool/releases/tag/latest | grep -o 'M4B_TOOL_DOWNLOAD_LINK=[^ ]*' | head -1 | cut -d '=' -f 2) \
    && wget "${M4B_TOOL_PRE_RELEASE_LINK}" -O /tmp/m4b-tool.tar.gz \
    && tar xzf /tmp/m4b-tool.tar.gz -C /tmp/ && rm /tmp/m4b-tool.tar.gz \
    && mv /tmp/m4b-tool.phar /usr/local/bin/m4b-tool-pre \
    && chmod +x /usr/local/bin/m4b-tool /usr/local/bin/m4b-tool-pre
WORKDIR ${WORKDIR}
CMD ["list"]
ENTRYPOINT ["m4b-tool

ok, it was something to do with ipv6. Adding --inet4-only to the wget commands worked