So in my last article I created a Docker container with nothing but a statically compiled helloworld in it. That demonstrated how it’s possible to define a very very (very very) simple container.
Here I define a similarly simple container with more complex dependencies – a hello world perl script requiring the Modern::Perl perl module. Now I don’t even need to build the executable binary, but all of a sudden I need to include enough of an environment to support my simple perl script.
As far as working with Docker this is not much more complex than changing “FROM scratch” to “FROM debian:latest”. The result is a much bigger container which will take more resources to run, but other than providing the computing resources to support that I really don’t have to care about it that much.
The Dockerfile now looks like this:
FROM debian:latest # Get base module requirements RUN apt-get --assume-yes update &&\ Â Â Â apt-get --assume-yes install libmodern-perl-perl # Copy the script in place and start running COPY hello.pl / CMD ["/hello.pl"]
But the container build process is no longer a couple of lines:
$ make docker docker build --rm -t bradhelloperl . Sending build context to Docker daemon 4.096 kB Sending build context to Docker daemon Step 0 : FROM debian:latest latest: Pulling from debian 902b87aaaec9: Already exists 9a61b6b1315e: Already exists Digest: sha256:b42e664a14b4ed96f7891103a6d0002a6ae2f09f5380c3171566bc5b6446a8ce Status: Downloaded newer image for debian:latest  ---> 9a61b6b1315e Step 1 : RUN apt-get --assume-yes update &&   apt-get --assume-yes install libmodern-perl-perl  ---> Running in afe73c43d3a8 Get:1 http://security.debian.org jessie/updates InRelease [63.1 kB] Get:2 http://security.debian.org jessie/updates/main amd64 Packages [165 kB] Get:3 http://httpredir.debian.org jessie InRelease [134 kB] Get:4 http://httpredir.debian.org jessie-updates InRelease [123 kB] Get:5 http://httpredir.debian.org jessie/main amd64 Packages [9038 kB] Get:6 http://httpredir.debian.org jessie-updates/main amd64 Packages [3614 B] Fetched 9527 kB in 40s (237 kB/s) Reading package lists... Reading package lists... Building dependency tree... Reading state information... The following extra packages will be installed:  libalgorithm-c3-perl libarchive-extract-perl libcgi-fast-perl libcgi-pm-perl  libclass-c3-perl libclass-c3-xs-perl libcpan-meta-perl libdata-optlist-perl  libdata-section-perl libfcgi-perl libgdbm3 liblog-message-perl  liblog-message-simple-perl libmodule-build-perl libmodule-pluggable-perl  libmodule-signature-perl libmro-compat-perl libpackage-constants-perl  libparams-util-perl libpod-latex-perl libpod-readme-perl  libregexp-common-perl libsoftware-license-perl libsub-exporter-perl  libsub-install-perl libterm-ui-perl libtext-soundex-perl  libtext-template-perl perl perl-modules rename Suggested packages:  perl-doc libterm-readline-gnu-perl libterm-readline-perl-perl make  libb-lint-perl libcpanplus-dist-build-perl libcpanplus-perl  libfile-checktree-perl libobject-accessor-perl Recommended packages:  libarchive-tar-perl The following NEW packages will be installed:  libalgorithm-c3-perl libarchive-extract-perl libcgi-fast-perl libcgi-pm-perl  libclass-c3-perl libclass-c3-xs-perl libcpan-meta-perl libdata-optlist-perl  libdata-section-perl libfcgi-perl libgdbm3 liblog-message-perl  liblog-message-simple-perl libmodern-perl-perl libmodule-build-perl  libmodule-pluggable-perl libmodule-signature-perl libmro-compat-perl  libpackage-constants-perl libparams-util-perl libpod-latex-perl  libpod-readme-perl libregexp-common-perl libsoftware-license-perl  libsub-exporter-perl libsub-install-perl libterm-ui-perl  libtext-soundex-perl libtext-template-perl perl perl-modules rename 0 upgraded, 32 newly installed, 0 to remove and 1 not upgraded. Need to get 6606 kB of archives. After this operation, 37.3 MB of additional disk space will be used. Get:1 http://httpredir.debian.org/debian/ jessie/main libgdbm3 amd64 1.8.3-13.1 [30.0 kB] Get:2 http://httpredir.debian.org/debian/ jessie/main libalgorithm-c3-perl all 0.09-1 [11.9 kB] Get:3 http://httpredir.debian.org/debian/ jessie/main libarchive-extract-perl all 0.72-1 [24.8 kB] Get:4 http://httpredir.debian.org/debian/ jessie/main perl-modules all 5.20.2-3+deb8u1 [2551 kB] Get:5 http://httpredir.debian.org/debian/ jessie/main perl amd64 5.20.2-3+deb8u1 [2629 kB] Get:6 http://httpredir.debian.org/debian/ jessie/main libcgi-pm-perl all 4.09-1 [213 kB] Get:7 http://httpredir.debian.org/debian/ jessie/main libparams-util-perl amd64 1.07-2+b1 [23.5 kB] Get:8 http://httpredir.debian.org/debian/ jessie/main libclass-c3-perl all 0.26-1 [22.9 kB] Get:9 http://httpredir.debian.org/debian/ jessie/main libsub-exporter-perl all 0.986-1 [49.9 kB] Get:10 http://httpredir.debian.org/debian/ jessie/main libdata-optlist-perl all 0.109-1 [10.6 kB] Get:11 http://httpredir.debian.org/debian/ jessie/main libclass-c3-xs-perl amd64 0.13-2+b1 [15.2 kB] Get:12 http://httpredir.debian.org/debian/ jessie/main libmodern-perl-perl all 1.20140107-1 [9964 B] Get:13 http://httpredir.debian.org/debian/ jessie/main libmodule-build-perl all 0.421000-2 [265 kB] Get:14 http://httpredir.debian.org/debian/ jessie/main libmodule-signature-perl all 0.73-1+deb8u2 [30.4 kB] Get:15 http://httpredir.debian.org/debian/ jessie/main libmodule-pluggable-perl all 5.1-1 [25.0 kB] Get:16 http://httpredir.debian.org/debian/ jessie/main libpackage-constants-perl all 0.04-1 [5820 B] Get:17 http://httpredir.debian.org/debian/ jessie/main libpod-latex-perl all 0.61-1 [34.7 kB] Get:18 http://httpredir.debian.org/debian/ jessie/main libregexp-common-perl all 2013031301-1 [173 kB] Get:19 http://httpredir.debian.org/debian/ jessie/main libpod-readme-perl all 0.11-1 [15.3 kB] Get:20 http://httpredir.debian.org/debian/ jessie/main libfcgi-perl amd64 0.77-1+b1 [39.1 kB] Get:21 http://httpredir.debian.org/debian/ jessie/main libsoftware-license-perl all 0.103010-3 [119 kB] Get:22 http://httpredir.debian.org/debian/ jessie/main libcgi-fast-perl all 1:2.04-1 [10.9 kB] Get:23 http://httpredir.debian.org/debian/ jessie/main libcpan-meta-perl all 2.142690-1 [125 kB] Get:24 http://httpredir.debian.org/debian/ jessie/main rename all 0.20-3 [12.4 kB] Get:25 http://httpredir.debian.org/debian/ jessie/main libsub-install-perl all 0.928-1 [11.4 kB] Get:26 http://httpredir.debian.org/debian/ jessie/main libmro-compat-perl all 0.12-1 [13.2 kB] Get:27 http://httpredir.debian.org/debian/ jessie/main libdata-section-perl all 0.200006-1 [13.4 kB] Get:28 http://httpredir.debian.org/debian/ jessie/main liblog-message-perl all 0.8-1 [26.0 kB] Get:29 http://httpredir.debian.org/debian/ jessie/main liblog-message-simple-perl all 0.10-2 [8126 B] Get:30 http://httpredir.debian.org/debian/ jessie/main libtext-template-perl all 1.46-1 [53.1 kB] Get:31 http://httpredir.debian.org/debian/ jessie/main libterm-ui-perl all 0.42-1 [19.1 kB] Get:32 http://httpredir.debian.org/debian/ jessie/main libtext-soundex-perl amd64 3.4-1+b2 [13.7 kB] debconf: delaying package configuration, since apt-utils is not installed Fetched 6606 kB in 16s (395 kB/s) Selecting previously unselected package libgdbm3:amd64. (Reading database ... 7528 files and directories currently installed.) Preparing to unpack .../libgdbm3_1.8.3-13.1_amd64.deb ... Unpacking libgdbm3:amd64 (1.8.3-13.1) ... Selecting previously unselected package perl-modules. Preparing to unpack .../perl-modules_5.20.2-3+deb8u1_all.deb ... Unpacking perl-modules (5.20.2-3+deb8u1) ... Selecting previously unselected package perl. Preparing to unpack .../perl_5.20.2-3+deb8u1_amd64.deb ... Unpacking perl (5.20.2-3+deb8u1) ... Selecting previously unselected package libalgorithm-c3-perl. Preparing to unpack .../libalgorithm-c3-perl_0.09-1_all.deb ... Unpacking libalgorithm-c3-perl (0.09-1) ... Selecting previously unselected package libarchive-extract-perl. Preparing to unpack .../libarchive-extract-perl_0.72-1_all.deb ... Unpacking libarchive-extract-perl (0.72-1) ... Selecting previously unselected package libcgi-pm-perl. Preparing to unpack .../libcgi-pm-perl_4.09-1_all.deb ... Unpacking libcgi-pm-perl (4.09-1) ... 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Setting up libgdbm3:amd64 (1.8.3-13.1) ... Setting up perl-modules (5.20.2-3+deb8u1) ... Setting up perl (5.20.2-3+deb8u1) ... update-alternatives: using /usr/bin/prename to provide /usr/bin/rename (rename) in auto mode Setting up libalgorithm-c3-perl (0.09-1) ... Setting up libarchive-extract-perl (0.72-1) ... Setting up libcgi-pm-perl (4.09-1) ... Setting up libfcgi-perl (0.77-1+b1) ... Setting up libcgi-fast-perl (1:2.04-1) ... Setting up libclass-c3-perl (0.26-1) ... Setting up libclass-c3-xs-perl (0.13-2+b1) ... Setting up libcpan-meta-perl (2.142690-1) ... Setting up libparams-util-perl (1.07-2+b1) ... Setting up libsub-install-perl (0.928-1) ... Setting up libdata-optlist-perl (0.109-1) ... Setting up libmro-compat-perl (0.12-1) ... Setting up libsub-exporter-perl (0.986-1) ... Setting up libdata-section-perl (0.200006-1) ... Setting up liblog-message-perl (0.8-1) ... Setting up liblog-message-simple-perl (0.10-2) ... Setting up libmodern-perl-perl (1.20140107-1) ... Setting up libmodule-build-perl (0.421000-2) ... Setting up libmodule-pluggable-perl (5.1-1) ... Setting up libmodule-signature-perl (0.73-1+deb8u2) ... Setting up libpackage-constants-perl (0.04-1) ... Setting up libpod-latex-perl (0.61-1) ... Setting up libregexp-common-perl (2013031301-1) ... Setting up libpod-readme-perl (0.11-1) ... Setting up libtext-template-perl (1.46-1) ... Setting up libsoftware-license-perl (0.103010-3) ... Setting up libterm-ui-perl (0.42-1) ... Setting up libtext-soundex-perl (3.4-1+b2) ... Setting up rename (0.20-3) ... update-alternatives: using /usr/bin/file-rename to provide /usr/bin/rename (rename) in auto mode Processing triggers for libc-bin (2.19-18) ...  ---> 5df0148ab594 Removing intermediate container afe73c43d3a8 Step 2 : COPY hello.pl /  ---> 73621b2beb17 Removing intermediate container 073772d52012 Step 3 : CMD /hello.pl  ---> Running in 32701bc83e03  ---> 2ba9eec0fbfa Removing intermediate container 32701bc83e03 Successfully built 2ba9eec0fbfa
And in this case I’ve create a perl script which loops forever to show what happens when a container keeps running:
#!/usr/bin/env perl
use Modern::Perl;
# autoflush output
$| = 1;
my $loop = 0;
while (1) {
   say "[${loop}] Hello World!";
   $loop++;
   sleep 1;
}
Now I start the container and ask it to run in the background:
$ make run docker run -d bradhelloperl e4cb410b97f18b70f18ba1a4b4ded3e310bc63f85dbaf58b776463ec4a61ab64
And to see what is being printed I view the container log:
 $ docker logs e4cb410b97f18b70f18ba1a4b4ded3e310bc63f85dbaf58b776463ec4a61ab64 [0] Hello World! [1] Hello World! [2] Hello World! [3] Hello World! [4] Hello World! [5] Hello World! [6] Hello World! [7] Hello World!
And finally, I’ll have to kill this container off now as it’s going to run forever. To show a different way this can be done I’ll look up the human readable ID and use it instead:
$ docker ps CONTAINER ID       IMAGE              COMMAND            CREATED            STATUS            PORTS              NAMES e4cb410b97f1       bradhelloperl      "/hello.pl"        4 minutes ago      Up 4 minutes                           silly_sinoussi $ docker kill silly_sinoussi silly_sinoussi $ docker rm silly_sinoussi silly_sinoussi
Note I needed to both kill and remove the container. While the container was killed but not removed I could still view the logs (and see the final stdout output before the kill was run).