Copy the frontend file of the official docker image to the dist of the web directory, modify the docker, shield the compiled dist part and establish soft links.
Dockerfile：

`

Built with arch: amd64 flavor: lxde image: ubuntu:20.04

################################################################################

base system

################################################################################

FROM ubuntu:20.04 as system

RUN sed -i 's#http://archive.ubuntu.com/ubuntu/#mirror://mirrors.ubuntu.com/mirrors.txt#' /etc/apt/sources.list;

built-in packages

ENV DEBIAN_FRONTEND noninteractive
RUN apt update
&& apt install -y --no-install-recommends software-properties-common curl apache2-utils
&& apt update
&& apt install -y --no-install-recommends --allow-unauthenticated
supervisor nginx sudo net-tools zenity xz-utils
dbus-x11 x11-utils alsa-utils
mesa-utils libgl1-mesa-dri
&& apt autoclean -y
&& apt autoremove -y
&& rm -rf /var/lib/apt/lists/*

install debs error if combine together

RUN apt update
&& apt install -y --no-install-recommends --allow-unauthenticated
xvfb x11vnc
vim-tiny firefox ttf-ubuntu-font-family ttf-wqy-zenhei
&& apt autoclean -y
&& apt autoremove -y
&& rm -rf /var/lib/apt/lists/*

RUN apt update
&& apt install -y gpg-agent
&& curl -LO https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
&& (dpkg -i ./google-chrome-stable_current_amd64.deb || apt-get install -fy)
&& curl -sSL https://dl.google.com/linux/linux_signing_key.pub | apt-key add
&& rm google-chrome-stable_current_amd64.deb
&& rm -rf /var/lib/apt/lists/*

RUN apt update
&& apt install -y --no-install-recommends --allow-unauthenticated
lxde gtk2-engines-murrine gnome-themes-standard gtk2-engines-pixbuf gtk2-engines-murrine arc-theme
&& apt autoclean -y
&& apt autoremove -y
&& rm -rf /var/lib/apt/lists/*

Additional packages require ~600MB

libreoffice pinta language-pack-zh-hant language-pack-gnome-zh-hant firefox-locale-zh-hant libreoffice-l10n-zh-tw

tini to fix subreap

ARG TINI_VERSION=v0.19.0
ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /bin/tini
RUN chmod x /bin/tini

ffmpeg

RUN apt update
&& apt install -y --no-install-recommends --allow-unauthenticated
ffmpeg
&& rm -rf /var/lib/apt/lists/*
&& mkdir /usr/local/ffmpeg
&& ln -s /usr/bin/ffmpeg /usr/local/ffmpeg/ffmpeg

python library

COPY rootfs/usr/local/lib/web/backend/requirements.txt /tmp/
RUN apt-get update
&& dpkg-query -W -f='${Package}\n' > /tmp/a.txt
&& apt-get install -y python3-pip python3-dev build-essential
&& pip3 install setuptools wheel && pip3 install -r /tmp/requirements.txt
&& ln -s /usr/bin/python3 /usr/local/bin/python
&& dpkg-query -W -f='${Package}\n' > /tmp/b.txt
&& apt-get remove -y diff --changed-group-format='%>' --unchanged-group-format='' /tmp/a.txt /tmp/b.txt | xargs
&& apt-get autoclean -y
&& apt-get autoremove -y
&& rm -rf /var/lib/apt/lists/*
&& rm -rf /var/cache/apt/* /tmp/a.txt /tmp/b.txt

################################################################################

builder

################################################################################
FROM ubuntu:20.04 as builder

RUN sed -i 's#http://archive.ubuntu.com/ubuntu/#mirror://mirrors.ubuntu.com/mirrors.txt#' /etc/apt/sources.list;

RUN apt-get update
&& apt-get install -y --no-install-recommends curl ca-certificates gnupg patch

nodejs

RUN curl -sL https://deb.nodesource.com/setup_12.x | bash -
&& apt-get install -y nodejs

yarn

RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
&& echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
&& apt-get update
&& apt-get install -y yarn

build frontend

COPY web /src/web
#RUN cd /src/web
#&& yarn
#&& yarn build
RUN sed -i 's#app/locale/#novnc/app/locale/#' /src/web/dist/static/novnc/app/ui.js

################################################################################

merge

################################################################################
FROM system
LABEL maintainer="[email protected]"
#RUN ls /src/web/dist/

COPY --from=builder /src/web/dist/ /usr/local/lib/web/frontend/
RUN ls /usr/local/lib/web/frontend/static/novnc/utils/websockify
COPY rootfs /
#RUN ln -sf /usr/local/lib/web/frontend/static/novnc/utils/websockify /usr/local/lib/web/frontend/static/websockify &&
#chmod x /usr/local/lib/web/frontend/static/websockify/run

EXPOSE 80
WORKDIR /root
ENV HOME=/home/ubuntu
SHELL=/bin/bash
HEALTHCHECK --interval=30s --timeout=5s CMD curl --fail http://127.0.0.1:6079/api/health
ENTRYPOINT ["/startup.sh"]
`

@gauravmeena83
I ran into the same problem, but this problem was solved with #187.

https://github.com/fcwu/docker-ubuntu-vnc-desktop/blob/develop/DEVELOPMENT.md

git clone --recursive https://github.com/fcwu/docker-ubuntu-vnc-desktop
or, if you have already cloned it, get submodules contents :
git submodule init; git submodule update