Update Dockerfile for reduce image size (#7556)

* Update Dockerfile for reduce image size

* Remove KUBE_VERSION form Dockerfile

Dockerfile

@@ -1,25 +1,30 @@
 # Use imutable image tags rather than mutable tags (like ubuntu:18.04)
 FROM ubuntu:bionic-20200807
 
-ENV KUBE_VERSION=v1.20.6
-
-RUN mkdir /kubespray
-WORKDIR /kubespray
-RUN apt update -y && \
-    apt install -y \
+RUN apt update -y \
+    && apt install -y \
     libssl-dev python3-dev sshpass apt-transport-https jq moreutils \
-    ca-certificates curl gnupg2 software-properties-common python3-pip rsync
-RUN curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - && \
-    add-apt-repository \
+    ca-certificates curl gnupg2 software-properties-common python3-pip rsync \
+    && rm -rf /var/lib/apt/lists/*
+RUN curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - \
+    && add-apt-repository \
     "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
     $(lsb_release -cs) \
     stable" \
-    && apt update -y && apt-get install docker-ce -y
+    && apt update -y && apt-get install --no-install-recommends -y docker-ce \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /kubespray
 COPY . .
-RUN /usr/bin/python3 -m pip install pip -U && /usr/bin/python3 -m pip install -r tests/requirements.txt && python3 -m pip install -r requirements.txt && update-alternatives --install /usr/bin/python python /usr/bin/python3 1
+RUN /usr/bin/python3 -m pip install pip -U \
+    && /usr/bin/python3 -m pip install -r tests/requirements.txt \
+    && python3 -m pip install -r requirements.txt \
+    && update-alternatives --install /usr/bin/python python /usr/bin/python3 1
 
-RUN curl -LO https://storage.googleapis.com/kubernetes-release/release/$KUBE_VERSION/bin/linux/amd64/kubectl \
-    && chmod a+x kubectl && cp kubectl /usr/local/bin/kubectl
+RUN KUBE_VERSION=$(sed -n 's/^kube_version: //p' roles/kubespray-defaults/defaults/main.yaml) \
+    && curl -LO https://storage.googleapis.com/kubernetes-release/release/$KUBE_VERSION/bin/linux/amd64/kubectl \
+    && chmod a+x kubectl \
+    && mv kubectl /usr/local/bin/kubectl
 
 # Some tools like yamllint need this
 ENV LANG=C.UTF-8