What is the difference between the COPY and ADD commands in a Dockerfile

Question

What is the difference between the COPY and ADD commands in a Dockerfile  and when would I use one over the other   COPY  lt src gt   lt dest gt       The COPY instruction will copy new files from  lt src gt  and add them to the container s filesystem at path  lt dest gt    ADD  lt src gt   lt dest gt       The ADD instruction will copy new files from  lt src gt  and add them to the container s filesystem at path  lt dest gt

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Important Note  I had to COPY and untar java package in my docker image  When I compared the docker image size created using ADD it was 180MB bigger than the one created using COPY  tar -xzf   tar gz and rm   tar gz  This means that although ADD removes the tar file  it is still kept somewhere  And its making the image bigger

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Source  https   nickjanetakis com blog docker-tip-2-the-difference-between-copy-and-add-in-a-dockerile   COPY and ADD are both Dockerfile instructions that serve similar purposes  They let you copy files from a specific location into a Docker image  COPY takes in a src and destination  It only lets you copy in a local file or directory from your host  the machine building the Docker image  into the Docker image itself  ADD lets you do that too  but it also supports 2 other sources  First  you can use a URL instead of a local file   directory  Secondly  you can extract a tar file from the source directly into the destination A valid use case for ADD is when you want to extract a local tar file into a specific directory in your Docker image  If you   re copying in local files to your Docker image  always use COPY because it   s more explicit

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Since Docker 17 05 COPY is used with the --from flag in multi-stage builds to copy artifacts from previous build stages to the current build stage   from the documentation     Optionally COPY accepts a flag --from  lt name index gt  that can be used to set the source location to a previous build stage  created with FROM    AS   that will be used instead of a build context sent by the user

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You should check the ADD and COPY documentation for a more detailed description of their behaviors  but in a nutshell  the major difference is that ADD can do more than COPY   ADD allows  lt src gt  to be a URL Referring to comments below  the ADD documentation states that    If  is a local tar archive in a recognized compression format  identity  gzip  bzip2 or xz  then it is unpacked as a directory  Resources from remote URLs are not decompressed   Note that the Best practices for writing Dockerfiles suggests using COPY where the magic of ADD is not required  Otherwise  you  since you had to look up this answer  are likely to get surprised someday when you mean to copy keep this archive intact tar gz into your container  but instead  you spray the contents onto your filesystem

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COPY copies a file directory from your host to your image   ADD copies a file directory from your host to your image  but can also fetch remote URLs  extract TAR files  etc      Use COPY for simply copying files and or directories into the build context    Use ADD for downloading remote resources  extracting TAR files  etc

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There is some official documentation on that point  Best Practices for Writing Dockerfiles      Because image size matters  using ADD to fetch packages from remote URLs is strongly discouraged  you should use curl or wget instead  That way you can delete the files you no longer need after they ve been extracted and you won t have to add another layer in your image    RUN mkdir -p  usr src things      amp  amp  curl -SL http   example com big tar gz         tar -xJC  usr src things      amp  amp  make -C  usr src things all      For other items  files  directories  that do not require ADD   s tar auto-extraction capability  you should always use COPY

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COPY is     Same as  ADD   but without the tar and remote URL handling    Reference straight from the source code

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docker build -t  image name  -v  host directory   temp build directory      This is another way to copy files into an image  The -v option temporarily creates a volume that us used during the build process     This is different that other volumes because it mounts a host directory for the build only   Files can be copied using a standard cp command     Also  like the curl and wget  it can be run in a command stack  runs in a single container  and not multiply the image size   ADD and COPY are not stackable because they run in a standalone container and subsequent commands on those files that execute in additional containers will multiply the image size   With the options set thus   -v  opt mysql-staging  tvol   The following will execute in one container   RUN cp -r  tvol mysql-5 7 15-linux-glibc2 5-x86 64  u1  amp  amp        mv  u1 mysql-5 7 15-linux-glibc2 5-x86 64  u1 mysql  amp  amp         mkdir  u1 mysql mysql-files  amp  amp        mkdir  u1 mysql innodb  amp  amp        mkdir  u1 mysql innodb libdata  amp  amp        mkdir  u1 mysql innodb innologs  amp  amp        mkdir  u1 mysql tmp  amp  amp         chmod 750  u1 mysql mysql-files  amp  amp        chown -R mysql  u1 mysql  amp  amp        chgrp -R mysql  u1 mysql

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From Docker docs   ADD or COPY Although ADD and COPY are functionally similar  generally speaking  COPY is preferred  That   s because it   s more transparent than ADD  COPY only supports the basic copying of local files into the container  while ADD has some features  like local-only tar extraction and remote URL support  that are not immediately obvious  Consequently  the best use for ADD is local tar file auto-extraction into the image  as in ADD rootfs tar xz     More  Best practices for writing Dockerfiles

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When creating a Dockerfile  there are two commands that you can use to copy files directories into it     ADD and COPY  Although there are slight differences in the scope of their function  they essentially perform the same task   So  why do we have two commands  and how do we know when to use one or the other   DOCKER ADD COMMAND  Let   s start by noting that the ADD command is older than COPY  Since the launch of the Docker platform  the ADD instruction has been part of its list of commands   The command copies files directories to a file system of the specified container   The basic syntax for the ADD command is   ADD  lt src gt       lt dest gt    It includes the source you want to copy   lt src gt   followed by the destination where you want to store it   lt dest gt    If the source is a directory  ADD copies everything inside of it  including file system metadata    For instance  if the file is locally available and you want to add it to the directory of an image  you type   ADD  source file path   destination path   ADD can also copy files from a URL  It can download an external file and copy it to the wanted destination  For example   ADD http   source file url   destination path   An additional feature is that it copies compressed files  automatically extracting the content in the given destination  This feature only applies to locally stored compressed files directories   ADD source file tar gz  temp   Bear in mind that you cannot download and extract a compressed file directory from a URL  The command does not unpack external packages when copying them to the local filesystem   DOCKER COPY COMMAND  Due to some functionality issues  Docker had to introduce an additional command for duplicating content     COPY   Unlike its closely related ADD command  COPY only has only one assigned function  Its role is to duplicate files directories in a specified location in their existing format  This means that it doesn   t deal with extracting a compressed file  but rather copies it as-is   The instruction can be used only for locally stored files  Therefore  you cannot use it with URLs to copy external files to your container   To use the COPY instruction  follow the basic command format   Type in the source and where you want the command to extract the content as follows   COPY  lt src gt       lt dest gt     For example   COPY  source file path   destination path    Which command to use  Best Practice   Considering the circumstances in which the COPY command was introduced  it is evident that keeping ADD was a matter of necessity  Docker released an official document outlining best practices for writing Dockerfiles  which explicitly advises against using the ADD command   Docker   s official documentation notes that COPY should always be the go-to instruction as it is more transparent than ADD   If you need to copy from the local build context into a container  stick to using COPY   The Docker team also strongly discourages using ADD to download and copy a package from a URL  Instead  it   s safer and more efficient to use wget or curl within a RUN command  By doing so  you avoid creating an additional image layer and save space

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From Docker docs  https   docs docker com engine userguide eng-image dockerfile best-practices  add-or-copy   Although ADD and COPY are functionally similar  generally speaking  COPY is preferred  That   s because it   s more transparent than ADD  COPY only supports the basic copying of local files into the container  while ADD has some features  like local-only tar extraction and remote URL support  that are not immediately obvious  Consequently  the best use for ADD is local tar file auto-extraction into the image  as in ADD rootfs tar xz     If you have multiple Dockerfile steps that use different files from your context  COPY them individually  rather than all at once  This will ensure that each step   s build cache is only invalidated  forcing the step to be re-run  if the specifically required files change   For example    COPY requirements txt  tmp   RUN pip install --requirement  tmp requirements txt  COPY    tmp    Results in fewer cache invalidations for the RUN step  than if you put the COPY    tmp  before it   Because image size matters  using ADD to fetch packages from remote URLs is strongly discouraged  you should use curl or wget instead  That way you can delete the files you no longer need after they   ve been extracted and you won   t have to add another layer in your image  For example  you should avoid doing things like    ADD http   example com big tar xz  usr src things   RUN tar -xJf  usr src things big tar xz -C  usr src things  RUN make -C  usr src things all   And instead  do something like    RUN mkdir -p  usr src things         amp  amp  curl -SL htt p   example com big tar xz          tar -xJC  usr src things         amp  amp  make -C  usr src things all   For other items  files  directories  that do not require ADD   s tar auto-extraction capability  you should always use COPY

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ADD instruction copies files or folders from a local or remote source and adds them to the container s file system  It used to copy local files  those must be in the working directory  ADD instruction unpacks local  tar files to the destination image directory  Example ADD http   someserver com filename pdf  var www html  COPY copies files from the working directory and adds them to the container s file system  It is not possible to copy a remote file using its URL with this Dockerfile instruction  Example COPY Gemfile Gemfile lock    COPY   src   var www html

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ADD and COPY both have same functionality of copying files and directories from source to destination but ADD has extra of file extraction and URL file extraction functionality  The best practice is to use COPY in only copy operation only avoid ADD is many areas  The link will explain it with some simple examples difference between COPY and ADD in dockerfile

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If you want to add a xx tar gz to a  usr local in container  unzip it  and then remove the useless compressed package   For COPY   COPY resources jdk-7u79-linux-x64 tar gz  tmp  RUN tar -zxvf  tmp jdk-7u79-linux-x64 tar gz -C  usr local RUN rm  tmp jdk-7u79-linux-x64 tar gz   For ADD   ADD resources jdk-7u79-linux-x64 tar gz  usr local    ADD supports local-only tar extraction  Besides it  COPY will use three layers  but ADD only uses one layer

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Let s say you have a tar file and you want to uncompress it after placing it in your container  remove it  you can use the COPY command to do this  Butt he various commands would be 1  Copy the tar file to the destination  2   Uncompress it  3  Remove the tar file  If you did this in 3 steps then there will be a new image created after each step  You can do this in one step using  amp  but it becomes a hassle  But you used ADD  then Docker will take care of everything for you and only one intermediate image will be created

[docker] What is the difference between the 'COPY' and 'ADD' commands in a Dockerfile?

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