在容器启动时，运行脚本来设置全局环境变量

Question

I am trying to create a docker image that will run a script when it starts. I want that script to reach out and get the public IP address of the container (simple curl call) and then set the returned address as an environmental variable that other programs can access.

I had tried setting the script to run on launch using a CMD in the Dockerfile, and while that executed the script it did not pass the variable out of the script into the system environment. I had tried using CMD./startup.sh as well as CMD. /var/www/html/startup.sh I also tried using variations of the the exec form CMD ["sh" "startup.sh"] but even when sourcing the script it would not pass the variable to the system.

Doing some reading people suggested trying to set the script as the entry point so I tried ENTRYPOINT [ "sh", "/var/www/html/s3_pull.sh" ] and ENTRYPOINT. /var/www/html/s3_pull.sh ENTRYPOINT. /var/www/html/s3_pull.sh

And while these run the script and I can see that the curl call is working and the variable is being set in the script. It does not pass that variable to the system.

The script Startup.sh is

#!/bin/bash

export FQDN=$(curl checkip.amazonaws.com)
echo $FQDN

exec "$@"

Output from the script (resulting ip address is censored here but comes back correct)

% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    14  100    14    0     0    103      0 --:--:-- --:--:-- --:--:--   103
108.---.---.---

currently my Dockerfile is

FROM mediawiki:latest
WORKDIR /var/www/html/
ADD Image-mods-AWS.sh ./
ADD startup.sh ./
RUN bash /var/www/html/Image-mods-AWS.sh
ENTRYPOINT [ "/bin/bash", "/var/www/html/startup.sh" ]
CMD apache2-foreground

The image-mods-AWS script installs Nano and the AWS CLI and sets the startup.sh as executable

The container runs on Debian 11 and the main process is apache2-foreground.

I'm fairly new to Linux and containers but my understanding of the problem is that the shell used to execute the script is a child process and as such cant pass its variables up to the parent shell. So I need to have the parent shell execute it. Which lead me to trying the dot space slash ". /" execution which works if I log into the container and run it manually from the command line, but doesn't work when used in the Dockerfile as either a CMD or ENTRYPOINT.

Is what I want to do even possible? and does anyone have any suggestions on how to get this to run and pass the variable to the system on launch.

---

EDIT:

When running the command

docker run --rm [container-name:tag] env

The output is

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    14  100    14    0     0     97      0 --:--:-- --:--:-- --:--:--    97
108.---.---.---

HOSTNAME=----
PHP_VERSION=7.4.29
APACHE_CONFDIR=/etc/apache2
PHP_INI_DIR=/usr/local/etc/php
GPG_KEYS=----
PHP_LDFLAGS=-Wl,-O1 -pie
PWD=/var/www/html
HOME=/root
MEDIAWIKI_MAJOR_VERSION=1.37
MEDIAWIKI_VERSION=1.37.2
PHP_SHA256=----
PHPIZE_DEPS=autoconf dpkg-dev file g++ gcc libc-dev make pkg-config re2c
PHP_URL=https://www.php.net/distributions/php-7.4.29.tar.xz
SHLVL=0
PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
APACHE_ENVVARS=/etc/apache2/envvars
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PHP_ASC_URL=https://www.php.net/distributions/php-7.4.29.tar.xz.asc
PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
FQDN=108.---.---.---

When doing this the container starts, prints the environment, then exits. it does however show that it is running the script and assigning the variable.

When running the container with the command

docker run --rm [container-name:tag]

The output is

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    14  100    14    0     0     57      0 --:--:-- --:--:-- --:--:--    57
108.---.---.---

AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message
[Thu Jul 14 00:13:39.367797 2022] [mpm_prefork:notice] [pid 9] AH00163: Apache/2.4.53 (Debian) PHP/7.4.29 configured -- resuming normal operations
[Thu Jul 14 00:13:39.367861 2022] [core:notice] [pid 9] AH00094: Command line: 'apache2 -D FOREGROUND'

Then Running the command 'env' gives the following output

MEDIAWIKI_VERSION=1.37.2
APACHE_CONFDIR=/etc/apache2
HOSTNAME=----
PHP_INI_DIR=/usr/local/etc/php
MEDIAWIKI_MAJOR_VERSION=1.37
HOME=/root
PHP_LDFLAGS=-Wl,-O1 -pie
PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PHP_VERSION=7.4.29
GPG_KEYS=----
PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PHP_ASC_URL=https://www.php.net/distributions/php-7.4.29.tar.xz.asc
PHP_URL=https://www.php.net/distributions/php-7.4.29.tar.xz
TERM=xterm
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PHPIZE_DEPS=autoconf dpkg-dev file g++ gcc libc-dev make pkg-config re2c
PWD=/var/www/html
PHP_SHA256=----
APACHE_ENVVARS=/etc/apache2/envvars

Which does not show the variable as part of the enviroment

Finally pushing the image up to AWS and running on ECS-Fargate and using the 'env' command gives the following output

S3_CONFIG_BUCKET=----
MEDIAWIKI_VERSION=1.37.2
APACHE_CONFDIR=/etc/apache2
PHP_INI_DIR=/usr/local/etc/php
HOSTNAME=----.compute.internal
MEDIAWIKI_MAJOR_VERSION=1.37
HOME=/root
PHP_LDFLAGS=-Wl,-O1 -pie
AWS_CONTAINER_CREDENTIALS_RELATIVE_URI=/v2/credentials/----
PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
AWS_EXECUTION_ENV=AWS_ECS_FARGATE
PHP_VERSION=7.4.29
GPG_KEYS=----
PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PHP_ASC_URL=https://www.php.net/distributions/php-7.4.29.tar.xz.asc
AWS_DEFAULT_REGION=----
PHP_URL=https://www.php.net/distributions/php-7.4.29.tar.xz
ECS_CONTAINER_METADATA_URI_V4=----
TERM=xterm-256color
ECS_CONTAINER_METADATA_URI=----
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
S3_LOGO_FILE=wiki.png
LANG=C.UTF-8
AWS_REGION=----
PHPIZE_DEPS=autoconf dpkg-dev file g++ gcc libc-dev make pkg-config re2c
PWD=/var/www/html
PHP_SHA256=----
APACHE_ENVVARS=/etc/apache2/envvars
S3_CONFIG_FILE=----

which also does not show the variable being saved to the environment

Answer 1

try using source when running your script like this:

$ source ./startup.sh

I'm not sure how it should be done under Dockerfile but try this:

ENTRYPOINT [ "source", "/var/www/html/startup.sh" ]