每个 docker 镜像都由一系列层组成。
例如：custom-elasticsearch:lastest
$: docker history custom-elasticsearch
IMAGE CREATED CREATED BY SIZE COMMENT
5f14f49e0f6b 8 days ago /bin/sh -c #(nop) EXPOSE 9091/tcp 9200/tcp 9 0 B
c1b5b6bdc8d8 8 days ago /bin/sh -c /usr/share/elasticsearch/bin/plugi 3 MB
a406ab7ba4ed 8 days ago /bin/sh -c #(nop) COPY file:cf296a4961a04abc0 489 B
6b0d046baaa8 8 days ago /bin/sh -c #(nop) COPY file:81c04951307f0688f 83 B
6f609da577b7 20 months ago /bin/sh -c #(nop) CMD ["elasticsearch"] 0 B
<missing> 20 months ago /bin/sh -c #(nop) EXPOSE 9200/tcp 9300/tcp 0 …