&gt; If I add a secret file in my first layer, then use the secret file in
&gt; my second layer, and the finally remove my secret file in the third
&gt; layer, and then build with the --squash flag.
&gt; 
&gt; Will there be any way now to get the secret file?

**Answer:** Your image **won&#39;t have** the secret file.

How `--squash` works:

Once the build is complete, Docker creates a new image loading the diffs from each layer into a single new layer and references all the parent&#39;s layers.

In other words: when squashing, Docker will take all the filesystem layers produced by a build and collapse them into a single new layer.

This can simplify the process of creating minimal container images, but may result in slightly higher overhead when images are moved around (because squashed layers can no longer be shared between images). Docker still caches individual layers to make subsequent builds fast.

Please note this feature squashes all the newly built layers into a single layer, it is not squashing to scratch.

**Side notes:**

Docker 1.13 also has support for compressing the build context that is sent from CLI to daemon using the `--compress` flag. This will speed up builds done on remote daemons by reducing the amount of data sent.

Please note as of Docker 1.13 this feature is experimental.

Say, we are using React with ES6. We import React and Component as

    import React from &#39;react&#39;
    import { Component } from &#39;react&#39;

Why the syntax difference? Can&#39;t we use as specified below?
   
    import Component from &#39;react&#39;




Difference between import React and import { Component } syntax

First of all my main purpose is to setup the IP and Port for my application dynamically.

I&#39;m using `IConfiguration` to inject a json config file, like some tutorial mentioned.

However, I can&#39;t retrieve the configuration in Program.cs, because my `WebHostBuilder` will use the StartUp and Url at the same time.

So at the time the host build up, there is nothing in my configuration.

    WebProtocolSettings settings_Web = new WebProtocolSettings();
    var host = new WebHostBuilder()
                    .UseIISIntegration()
                    .UseKestrel()
                    .UseContentRoot(Directory.GetCurrentDirectory())
                    .UseStartup&lt;Startup&gt;()
                    .UseUrls(settings_Web.Url + &quot;:&quot; + settings_Web.Port)
                    .Build();


In Startup.cs

    public Startup(IHostingEnvironment env)
    {
        // Set up configuration sources.
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile(&quot;appsettings.json&quot;, optional: true, reloadOnChange: true);

        Configuration = builder.Build();
    }

    public IConfigurationRoot Configuration { get; set; }

    public void ConfigureServices(IServiceCollection services)
    {
        // Adds services required for using options.
        services.AddOptions();

        var _WebProtocolSettings = Configuration.GetSection(&quot;WebProtocolSettings&quot;);

        // Register the IConfiguration instance
        services.Configure&lt;WebProtocolSettings&gt;(_WebProtocolSettings);
    }

My appsettings.json:

    {
        &quot;WebProtocolSettings&quot;: {
            &quot;Url&quot;: &quot;127.0.0.1&quot;,
            &quot;Port&quot;: 5050
        }
    }

My WebProtocolSettings.cs:

    public class WebProtocolSettings
    {
        public string Url { get; set; }
        public int Port { get; set; }
    }

Read appsettings.json in Main Program.cs

In **Docker 1.13** the new **--squash** parameter was added. 

I&#39;m now hoping to reduce the size of my images as well as being able to &quot;hide&quot; secret files I have in my layers. 

Below you can now see the difference from doing a build with and without the --squash parameter. 

**Without Squash**

[![enter image description here][1]][1]

**With Squash**

[![enter image description here][2]][2]


**Now to my question.** 

If I add a secret file in my **first** layer, then use the secret file in my **second** layer, and the finally remove my secret file in the **third** layer, and then build with the --squash flag.

Will there be **any way** now to get the secret file? 

  [1]: https://i.stack.imgur.com/ktjwg.jpg
  [2]: https://i.stack.imgur.com/wZQIQ.jpg

How does the new Docker --squash work

In Docker 1.13 the new --squash parameter was added.
I'm now hoping to reduce the size of my images as well as being able to "hide" secret files I have in my layers.
Below you can now see the difference from doing a build with and without the --squash parameter.
Without Squash
<a href="https://i.stack.imgur.com/ktjwg.jpg" target="_blank" rel="noopener noreferrer"><img src="https://i.stack.imgur.com/ktjwg.jpg" alt="enter image description here"></a>
With Squash
<a href="https://i.stack.imgur.com/wZQIQ.jpg" target="_blank" rel="noopener noreferrer"><img src="https://i.stack.imgur.com/wZQIQ.jpg" alt="enter image description here"></a>
Now to my question.
If I add a secret file in my first layer, then use the secret file in my second layer, and the finally remove my secret file in the third layer, and then build with the --squash flag.
Will there be any way now to get the secret file?

Here&#39;s the result when I type `docker ps` :
![here is the image when i type docker ps][1]


I have 3 docker containers: webapps, redis and rabbitmq. I want to link container webapps to container redis and rabbitmq container. In non docker apps, mywebapps can send message to rabbitmq and write/read redis.

I tried using command like this 

    docker run --name rabbitmq -p 8080:80 --link webapps:nimmis/apache-php7 -d rabbitmq

but it does not work.

Here is my config.php on webapps where I am trying to send messages via rabbitmq:

    define(&#39;HOST&#39;, &#39;localhost&#39;);
    define(&#39;PORT&#39;, 5672);

I tried to change localhost with hostname

    define(&#39;HOST&#39;, &#39;rabbitmq&#39;);
    define(&#39;PORT&#39;, 5672);

Error message says `connection refused`.

It seems that in my three containers needs to be configured in the same network namespace.

  [1]: https://i.stack.imgur.com/gD2jR.jpg

How to link containers in docker?

I am trying to pull the images I created and I get this error:

    /usr/local/bin/docker-compose up -d
    Pulling hub (dockyard.cloud.capitalone.com/entepriseatdd/selenium-hub:3.0.0)...
    Trying to pull repository dockyard.cloud.capitalone.com/entepriseatdd/selenium-hub ...
    ERROR: manifest unknown: manifest unknown
    We are Spinning up 2 Browsers.
    /usr/local/bin/docker-compose scale chrome=2 firefox=2
    Creating and starting execution_chrome_1 ...
    Creating and starting execution_chrome_2 ...
    Pulling chrome (dockyard.cloud.capitalone.com/entepriseatdd/selenium-chrome-node:53.0.3)...
    Pulling chrome (dockyard.cloud.capitalone.com/entepriseatdd/selenium-chrome-node:53.0.3)...
    Trying to pull repository dockyard.cloud.capitalone.com/entepriseatdd/selenium-chrome-node ... 
    Trying to pull repository dockyard.cloud.capitalone.com/entepriseatdd/selenium-chrome-node ...
 
    ERROR: for execution_chrome_1  manifest unknown: manifest unknown

    ERROR: for execution_chrome_2  manifest unknown: manifest unknown


DOCKER manifest unknown: manifest unknown

This could be maybe a trivial question but reading docs for [ARG][1] and [ENV][2] doesn&#39;t put things clear to me.

I am building a PHP-FPM container and I want to give the ability for enable/disable some extensions on user needs. 

Would be great if this could be done in the Dockerfile by adding conditionals and passing flags on the build command perhaps but AFAIK is not supported.

In my case and my personal approach is to run a small script when container starts, something like the following:

    #!/bin/sh   
    set -e
    
    RESTART=&quot;false&quot;
    
    # This script will be placed in /config/init/ and run when container starts.
    if  [ &quot;$INSTALL_XDEBUG&quot; == &quot;true&quot; ]; then
        printf &quot;\nInstalling Xdebug ...\n&quot;
        yum install -y  php71-php-pecl-xdebug
        RESTART=&quot;true&quot;
    fi
    ...   
    if  [ &quot;$RESTART&quot; == &quot;true&quot; ]; then
        printf &quot;\nRestarting php-fpm ...\n&quot;
        supervisorctl restart php-fpm
    fi
    
    exec &quot;$@&quot;

This is how my `Dockerfile` looks like:

    FROM reynierpm/centos7-supervisor
    ENV TERM=xterm \
        PATH=&quot;/root/.composer/vendor/bin:${PATH}&quot; \
        INSTALL_COMPOSER=&quot;false&quot; \
        COMPOSER_ALLOW_SUPERUSER=1 \
        COMPOSER_ALLOW_XDEBUG=1 \
        COMPOSER_DISABLE_XDEBUG_WARN=1 \
        COMPOSER_HOME=&quot;/root/.composer&quot; \
        COMPOSER_CACHE_DIR=&quot;/root/.composer/cache&quot; \
        SYMFONY_INSTALLER=&quot;false&quot; \
        SYMFONY_PROJECT=&quot;false&quot; \
        INSTALL_XDEBUG=&quot;false&quot; \
        INSTALL_MONGO=&quot;false&quot; \
        INSTALL_REDIS=&quot;false&quot; \
        INSTALL_HTTP_REQUEST=&quot;false&quot; \
        INSTALL_UPLOAD_PROGRESS=&quot;false&quot; \
        INSTALL_XATTR=&quot;false&quot;
    
    RUN yum install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm \
                       https://rpms.remirepo.net/enterprise/remi-release-7.rpm
    RUN yum install -y  \
            yum-utils \
            git \
            zip \
            unzip \
            nano \
            wget \
            php71-php-fpm \
            php71-php-cli \
            php71-php-common \
            php71-php-gd \
            php71-php-intl \
            php71-php-json \
            php71-php-mbstring \
            php71-php-mcrypt \
            php71-php-mysqlnd \
            php71-php-pdo \
            php71-php-pear \
            php71-php-xml \
            php71-pecl-apcu \
            php71-php-pecl-apfd \
            php71-php-pecl-memcache \
            php71-php-pecl-memcached \
            php71-php-pecl-zip &amp;&amp; \
            yum clean all &amp;&amp; rm -rf /tmp/yum*
    
    RUN ln -sfF /opt/remi/php71/enable /etc/profile.d/php71-paths.sh &amp;&amp; \
        ln -sfF /opt/remi/php71/root/usr/bin/{pear,pecl,phar,php,php-cgi,phpize} /usr/local/bin/. &amp;&amp; \
        mv -f /etc/opt/remi/php71/php.ini /etc/php.ini &amp;&amp; \
        ln -s /etc/php.ini /etc/opt/remi/php71/php.ini &amp;&amp; \
        rm -rf /etc/php.d &amp;&amp; \
        mv /etc/opt/remi/php71/php.d /etc/. &amp;&amp; \
        ln -s /etc/php.d /etc/opt/remi/php71/php.d
    
    COPY container-files /
    RUN chmod +x /config/bootstrap.sh
    WORKDIR /data/www
    EXPOSE 9001

Currently this is working but ... If I want to add let&#39;s say 20 (a random number) of extensions or any other feature that can be enable|disable then I will end with 20 non necessary `ENV` (because Dockerfile doesn&#39;t support .env files) definition whose only purpose would be set this flag for let the script knows what to do then ...

- Is this the right way to do it? 
- Should I use `ENV` for this purpose? 

I am open to ideas if you have a different approach for achieve this please let me know about it


  [1]: https://docs.docker.com/engine/reference/builder/#arg
  [2]: https://docs.docker.com/engine/reference/builder/#env

ARG or ENV, which one to use in this case?

Below is the content of my &quot;Dockerfile&quot; 

```docker file
FROM node:boron

# Create app directory
RUN mkdir -p /usr/src/app

# Change working dir to /usr/src/app
WORKDIR /usr/src/app

VOLUME . /usr/src/app

RUN npm install

EXPOSE 8080

CMD [&quot;node&quot; , &quot;server&quot; ]
```

In this file I am expecting `VOLUME . /usr/src/app` instruction to mount
contents of present working directory in host to be mounted on `/usr/src/app`
folder of container.

Please let me know if this is the correct way?

Understanding &quot;VOLUME&quot; instruction in DockerFile

Here&#39;s my docker-compose:

    version: &#39;2&#39;
    services:
      couchpotato:
        build:
            context: ./couchpotato
            dockerfile: Dockerfile
        ports:
         - 5050:5050
        volumes:
         - &quot;${PWD}/couchpotato/data:/home/CouchPotato/data/&quot;
         - &quot;${PWD}/couchpotato/config:/home/CouchPotato/config/&quot;

When I run it inside the shell, in the directory of the docker-compose.yml, I get:

    WARNING: The PWD variable is not set. Defaulting to a blank string.
and the compose starts with PWD being empty. 

I don&#39;t see any error in the file, as seen here: https://docs.docker.com/compose/environment-variables/

Docker compose won&#39;t find $PWD environment variable

I am following [this link][1] to create my first docker Image and it went successfully and now I am trying to push this Image into my docker repository from this [link][2]. But whenever I am trying to push this Image into repository , I  got this type of error. 

    denied: requested access to the resource is denied

[![enter image description here][3]][3]

Could anyone give me some hint towards this problem ? Any help would appreciated.

Note: I have successfully login into docker 

  [1]: https://docs.docker.com/engine/getstarted/step_four/
  [2]: https://docs.docker.com/engine/getstarted/step_six/
  [3]: https://i.stack.imgur.com/GCu19.png

denied: requested access to the resource is denied : docker

I&#39;m trying to use docker to automate maven builds. The project I want to build takes nearly 20 minutes to download all the dependencies, so I tried to build a docker image that would cache these dependencies, but it doesn&#39;t seem to save it. My Dockerfile is

    FROM maven:alpine
    RUN mkdir -p /usr/src/app
    WORKDIR /usr/src/app
    ADD pom.xml /usr/src/app
    RUN mvn dependency:go-offline

The image builds, and it does download everything. However, the resulting image is the same size as the base `maven:alpine` image, so it doesn&#39;t seem to have cached the dependencies in the image. When I try to use the image to `mvn compile` it goes through the full 20 minutes of redownloading everything.

Is it possible to build a maven image that caches my dependencies so they don&#39;t have to download everytime I use the image to perform a build?

I&#39;m running the following commands:

    docker build -t my-maven .

    docker run -it --rm --name my-maven-project -v &quot;$PWD&quot;:/usr/src/mymaven -w /usr/src/mymaven my-maven mvn compile

My understanding is that whatever `RUN` does during the docker build process becomes part of the resulting image.

Maven docker cache dependencies

I want to setup some configuration when my container starts, for this I am using shell scripts. But my container will exits as soon as my scripts ends, I have tried with -d flag / detached mode but It will never run in detached mode.

Below is my Dockerfile

    FROM ubuntu:14.04

    ADD shell.sh /usr/local/bin/shell.sh

    RUN chmod 777 /usr/local/bin/shell.sh

    CMD /usr/local/bin/shell.sh

Below is my shell script

    #!/bin/bash
    echo Hello-docker

1. Run without any flag

        docker run hello-docker
This will print &#39;Hello-docker&#39; on my console and exits
2. Run with -itd flags

        docker run -itd hello-docker
and as below my console output, This time also will exits soon.  **:(**
[![enter image description here][1]][1]

 - The difference I saw is in COMMAND section when I run other images command section will shows &quot;/bin/bash&quot; and will continue in detached mode.

 - And when I run my image in container with shell script COMMAND section will show &quot;/bin/sh -c /usr/loca&quot;, and Exit.

 - I want to run container till I not stop it manually.

EDIT:

After adding ENTRYPOINT instruction in Dockerfile, this will not execute my shell script :(

    FROM ubuntu:14.04

    ADD shell.sh /usr/local/bin/shell.sh

    RUN chmod 777 /usr/local/bin/shell.sh

    CMD /usr/local/bin/shell.sh
    
    ENTRYPOINT /bin/bash
As per docker documentation [here][2]

CMD will be overridden when running the container with alternative arguments, so If I run docker image with some arguments as below, will not execute CMD instructions. :(

    sudo docker run -it --entrypoint=/bin/bash &lt;imagename&gt;
  [1]: https://i.stack.imgur.com/gXaRd.png
  [2]: https://docs.docker.com/engine/reference/builder/#understand-how-cmd-and-entrypoint-interact

Content Type	Original Author	Original Content on Stackoverflow
Question	Fore	View Question on Stackoverflow
Solution 1 - Docker	Farhad Farahi	View Answer on Stackoverflow

How does the new Docker --squash work

Docker Problem Overview

Docker Solutions

Solution 1 - Docker

Read appsettings.json in Main Program.cs

Difference between import React and import { Component } syntax

Attributions