參考 https://www.cnblogs.com/CloudMan6/p/6839420.html     構建centos-wget 映象前本地沒有快取centos映象，在構建的第一步需要dokcer pull centos映象   [email protected]:~/docker# cat Dockerfile FROM centos RUN yum install -y wget [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE

[email protected]:~/111# docker build  -t centos-wget .      Sending build context to Docker daemon  2.048kB Step 1/2 : FROM centos latest: Pulling from library/centos a02a4930cb5d: Pull complete Digest: sha256:365fc7f33107869dfcf2b3ba220ce0aa42e16d3f8e8b3c21d72af1ee622f0cf0 Status: Downloaded newer image for centos:latest ---> 1e1148e4cc2c Step 2/2 : RUN yum install -y wget . . . .   構建centos-wget 映象前本地有快取centos映象，在構建的第一步直接使用本地快取，無需docker pull   [email protected]:~/docker# cat Dockerfile FROM centos RUN yum install -y wget [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE [email protected]:~/docker# docker pull centos Using default tag: latest latest: Pulling from library/centos a02a4930cb5d: Pull complete Digest: sha256:38777a4106f0072649128ea4236241345a3ed21c55abbbd53bad5342549f6126 Status: Downloaded newer image for centos:latest [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE centos              latest              1e1148e4cc2c        4 weeks ago         202MB [email protected]:~/docker# docker build -t centos-wget . Sending build context to Docker daemon  2.048kB Step 1/2 : FROM centos ---> 1e1148e4cc2c Step 2/2 : RUN yum install -y wget . . . .   繼續構建一個新的映象，比centos-wget多執行一個uptime，可以看到第一步和第二步直接使用的快取，並未重新構建   [email protected]:~/docker# cat Dockerfile FROM centos RUN yum install -y wget RUN uptime [email protected]:~/docker# docker build -t centos-uptime . Sending build context to Docker daemon  2.048kB Step 1/3 : FROM centos ---> 1e1148e4cc2c Step 2/3 : RUN yum install -y wget ---> Using cache ---> 31093d4c7d97 Step 3/3 : RUN uptime ---> Running in 303cb5e38dd3 16:35:42 up 203 days,  7:58,  0 users,  load average: 0.00, 0.00, 0.00 Removing intermediate container 303cb5e38dd3 ---> cb7f8bec5d08 Successfully built cb7f8bec5d08 Successfully tagged centos-uptime:latest [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE centos-uptime       latest              cb7f8bec5d08        11 seconds ago      272MB centos-wget         latest              31093d4c7d97        7 minutes ago       272MB centos              latest              1e1148e4cc2c        4 weeks ago         202MB   如果將yum和uptime兩個對調，則不會使用之前的 centos-wget 映象快取   [email protected]:~/docker# cat Dockerfile FROM centos RUN uptime RUN yum install -y wget [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE centos-uptime       latest              cb7f8bec5d08        5 minutes ago       272MB centos-wget         latest              31093d4c7d97        12 minutes ago      272MB centos              latest              1e1148e4cc2c        4 weeks ago         202MB [email protected]:~/docker# docker build -t centos-test . Sending build context to Docker daemon  2.048kB Step 1/3 : FROM centos ---> 1e1148e4cc2c Step 2/3 : RUN uptime ---> Running in 1724b8f64a50 16:41:11 up 203 days,  8:03,  0 users,  load average: 0.00, 0.02, 0.00 Removing intermediate container 1724b8f64a50 ---> 91a208dedb3d Step 3/3 : RUN yum install -y wget ---> Running in 85f7f29637d5 Loaded plugins: fastestmirror, ovl Determining fastest mirrors * base: mirrors.huaweicloud.com * extras: mirrors.huaweicloud.com * updates: mirrors.huaweicloud.com Resolving Dependencies --> Running transaction check ---> Package wget.x86_64 0:1.14-18.el7 will be installed --> Finished Dependency Resolution . . . . [email protected]:~/docker# docker images REPOSITORY          TAG                 IMAGE ID            CREATED              SIZE centos-test         latest              fc8b11ebfd31        About a minute ago   272MB centos-uptime       latest              cb7f8bec5d08        7 minutes ago        272MB centos-wget         latest              31093d4c7d97        14 minutes ago       272MB centos              latest              1e1148e4cc2c        4 weeks ago          202MB     總結：     1、構建映象時，FROM 中的映象如果本地有，就會直接使用本地快取     2、構建映象時，如果Dockerfile前N行與之前某映象構建時Dockerfile的前N行一樣，那將直接使用之前映象中的層，不比從頭開始構建。除非在docker build 中新增 --no-cache 引數