Problem Description
When I created configures and want to copy them into a docker image based on Nginx.[^1]
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| $ tree conf.d
conf.d
└── custom.conf
1 directory, 0 files
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I wrote a dockerfile shown below and built with it.
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| FROM nginx
COPY src/conf.d /etc/nginx/conf.d
RUN ls -l /etc/nginx/conf.d
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I found the file /etc/nginx/conf.d/default.conf which exists in the basic Nginx image was not removed in the built one.
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| $ docker build --no-cache .
Sending build context to Docker daemon 4.608kB
Step 1/3 : FROM nginx
---> 2622e6cca7eb
Step 2/3 : COPY src/conf.d /etc/nginx/conf.d
---> afb504ce8ba6
Step 3/3 : RUN ls -l /etc/nginx/conf.d
---> Running in 7aef205e795c
total 8
drwxr-xr-x 2 root root 4096 Jun 30 08:21 custom.conf
-rw-r--r-- 1 root root 1093 May 26 15:01 default.conf
Removing intermediate container 7aef205e795c
---> 604a79ae8a67
Successfully built 604a79ae8a67
|
Explaination
The document says:
The COPY instruction copies new files or directories from <src> and adds them to the filesystem of the container at the path <dest>.
The COPY command only copies all contents in the source directory but not the source directory itself.
Solution
The only way to resolve it is set the whole parent directory of conf.d as the <src> directory. The all contents except conf.d will be kept.[^2]
First, let us build our new configure stucture.
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| $ tree src
src
└── conf.d
└── custom.conf
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Then, change the dockerfile to show both /etc/nginx and /etc/nginx/conf.d directories.
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| FROM nginx
COPY src/conf.d /etc/nginx/conf.d
RUN ls -l /etc/nginx
RUN ls -l /etc/nginx/conf.d
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When build it with the new dockerfile.
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| $ docker build --no-cache .
Sending build context to Docker daemon 3.584kB
Step 1/4 : FROM nginx
---> 2622e6cca7eb
Step 2/4 : COPY src/conf.d /etc/nginx/conf.d
---> 882c7992707f
Step 3/4 : RUN ls -l /etc/nginx
---> Running in d0bf8116ec8a
total 40
drwxr-xr-x 1 root root 4096 Jun 30 08:53 conf.d
-rw-r--r-- 1 root root 1007 May 26 15:00 fastcgi_params
-rw-r--r-- 1 root root 2837 May 26 15:00 koi-utf
-rw-r--r-- 1 root root 2223 May 26 15:00 koi-win
-rw-r--r-- 1 root root 5231 May 26 15:00 mime.types
lrwxrwxrwx 1 root root 22 May 26 15:01 modules -> /usr/lib/nginx/modules
-rw-r--r-- 1 root root 643 May 26 15:01 nginx.conf
-rw-r--r-- 1 root root 636 May 26 15:00 scgi_params
-rw-r--r-- 1 root root 664 May 26 15:00 uwsgi_params
-rw-r--r-- 1 root root 3610 May 26 15:00 win-utf
Removing intermediate container d0bf8116ec8a
---> 5626761ee0b8
Step 4/4 : RUN ls -l /etc/nginx/conf.d
---> Running in a6597815965f
total 8
drwxr-xr-x 2 root root 4096 Jun 30 08:50 custom.conf
-rw-r--r-- 1 root root 1093 May 26 15:01 default.conf
Removing intermediate container a6597815965f
---> c3034a1a51fc
Successfully built c3034a1a51fc
|
We can see all files in /etc/nginx original is kept. And the directory /etc/nginx/conf.d is totally be overwritten.
By the way, If we want, we can add a new configure file src/nginx.conf. It will overwrite the /etc/nginx/nginx.conf in new images too.
References
[^1]: Full example which uses the bad practice here.
[^2]: Full example which uses the good practice here.