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Cuando empecé a trastear con docker, empecé a utilizar la imagen con la que más cómodo me sentía, ubuntu.
Conforme fuí adentrandome en este mundo, y viendo cómo otras personas construían sus contenedores, me dí cuenta que muchos de ellos usaban imágenes alpine.
Vamos a realizar una prueba, para descubrir porqué utilizar estas imágenes.
Para esto, vamos a levantar un contenedor ubuntu y un contenedor alpine y vamos a tirar un docker system df -v
REPOSITORY TAG IMAGE ID CREATED SIZE SHARED SIZE UNIQUE SIZE CONTAINERS
ubuntu latest 72300a873c2c 2 weeks ago 64.21MB 0B 64.21MB 1
alpine latest e7d92cdc71fe 7 weeks ago 5.591MB 0B 5.591MB 2
Cómo podemos ver, la imagen de ubuntu ocupa como unas 12 veces más que la imagen alpine. Lo que quiere decir, que a la hora de desplegar nuestros contenedores, si utilizamos la imagen alpine, esta se desplegará mucho más rápido.
Las imágenes alpine vienen con programas o comandos muy básicos, por ejemplo, en la imagen ubuntu, tenemos la shell sh y bash y en alpine sólo tenemos sh.
Cuando estás depurando, porque el programa que ejecuta tu contenedor no funciona como esperas, puede hacerse un poco tedioso utilizar una alpine, porque no vienen incluidas muchas herramientas o comandos básicos, como pueden ser ping, net-tools etc…, aunque oye!! nadie te dice que no puedas instalarlas.
Pero por otro lado, hay que tener en cuenta algo que leí una vez en algún lado:
Un buen programador introduce un error cada 100 líneas de código. Un programador excelente introduce un error cada 1000 líneas de código. (Algo así era, no lo recuerdo bien)
Esto quiere decir, que cuanto más software tenga el sistema en el que estemos trabajando, más errores y bugs contendrá, y más fácil será para un atacante entrar en el sistema.
Este es otro motivo por el cual es interesante utilizar estas imágenes minimalistas.
Ejemplo.
Vamos a instalar un apache2 en un alpine para ver que podemos utilizar estas imágenes para levantar un servidor web.
athos@athos-Z97P-D3:~$ docker run -it -p 80:80 alpine sh
/ # apk update
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/community/x86_64/APKINDEX.tar.gz
v3.11.3-113-g5cfecee709 [http://dl-cdn.alpinelinux.org/alpine/v3.11/main]
v3.11.3-112-gbfe51f74f3 [http://dl-cdn.alpinelinux.org/alpine/v3.11/community]
OK: 11268 distinct packages available
/ # apk add apache2
(1/6) Installing libuuid (2.34-r1)
(2/6) Installing apr (1.7.0-r0)
(3/6) Installing expat (2.2.9-r1)
(4/6) Installing apr-util (1.6.1-r6)
(5/6) Installing pcre (8.43-r0)
(6/6) Installing apache2 (2.4.41-r0)
Executing apache2-2.4.41-r0.pre-install
Executing busybox-1.31.1-r9.trigger
OK: 9 MiB in 20 packages
/ # exec /usr/sbin/httpd -D FOREGROUND
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.3. Set the 'ServerName' directive globally to suppress this message
Y ahora accedemos desde el navegador
Lo mismo vamos a hacer con una imagen ubuntu:
athos@athos-Z97P-D3:~$ docker run -it -p 80:80 ubuntu bash
root@08534d150381:/# apt update
Get:1 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
Get:2 http://archive.ubuntu.com/ubuntu bionic InRelease [242 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Get:4 http://security.ubuntu.com/ubuntu bionic-security/multiverse amd64 Packages [7641 B]
Get:5 http://archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
Get:6 http://security.ubuntu.com/ubuntu bionic-security/restricted amd64 Packages [31.0 kB]
Get:7 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages [836 kB]
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Get:9 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages [11.3 MB]
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Get:15 http://archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages [1351 kB]
Get:16 http://archive.ubuntu.com/ubuntu bionic-updates/multiverse amd64 Packages [11.7 kB]
Get:17 http://archive.ubuntu.com/ubuntu bionic-backports/main amd64 Packages [2496 B]
Get:18 http://archive.ubuntu.com/ubuntu bionic-backports/universe amd64 Packages [4247 B]
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Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
root@08534d150381:/# apt install apache2
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
apache2-bin apache2-data apache2-utils file libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libasn1-8-heimdal libexpat1 libgdbm-compat4
libgdbm5 libgssapi3-heimdal libhcrypto4-heimdal libheimbase1-heimdal libheimntlm0-heimdal libhx509-5-heimdal libicu60 libkrb5-26-heimdal libldap-2.4-2
libldap-common liblua5.2-0 libmagic-mgc libmagic1 libnghttp2-14 libperl5.26 libroken18-heimdal libsasl2-2 libsasl2-modules libsasl2-modules-db
libsqlite3-0 libssl1.1 libwind0-heimdal libxml2 mime-support netbase openssl perl perl-modules-5.26 ssl-cert xz-utils
Suggested packages:
www-browser apache2-doc apache2-suexec-pristine | apache2-suexec-custom ufw gdbm-l10n libsasl2-modules-gssapi-mit | libsasl2-modules-gssapi-heimdal
libsasl2-modules-ldap libsasl2-modules-otp libsasl2-modules-sql ca-certificates perl-doc libterm-readline-gnu-perl | libterm-readline-perl-perl make
openssl-blacklist
The following NEW packages will be installed:
apache2 apache2-bin apache2-data apache2-utils file libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libasn1-8-heimdal libexpat1
libgdbm-compat4 libgdbm5 libgssapi3-heimdal libhcrypto4-heimdal libheimbase1-heimdal libheimntlm0-heimdal libhx509-5-heimdal libicu60 libkrb5-26-heimdal
libldap-2.4-2 libldap-common liblua5.2-0 libmagic-mgc libmagic1 libnghttp2-14 libperl5.26 libroken18-heimdal libsasl2-2 libsasl2-modules
libsasl2-modules-db libsqlite3-0 libssl1.1 libwind0-heimdal libxml2 mime-support netbase openssl perl perl-modules-5.26 ssl-cert xz-utils
0 upgraded, 42 newly installed, 0 to remove and 0 not upgraded.
Need to get 21.0 MB of archives.
After this operation, 99.4 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
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Get:24 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libldap-common all 2.4.45+dfsg-1ubuntu1.4 [16.9 kB]
Get:25 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libldap-2.4-2 amd64 2.4.45+dfsg-1ubuntu1.4 [155 kB]
Get:26 http://archive.ubuntu.com/ubuntu bionic/main amd64 libaprutil1-ldap amd64 1.6.1-2 [8764 B]
Get:27 http://archive.ubuntu.com/ubuntu bionic/main amd64 liblua5.2-0 amd64 5.2.4-1.1build1 [108 kB]
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Get:29 http://archive.ubuntu.com/ubuntu bionic/main amd64 libicu60 amd64 60.2-3ubuntu3 [8054 kB]
Get:30 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libxml2 amd64 2.9.4+dfsg1-6.1ubuntu1.3 [663 kB]
Get:31 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 apache2-bin amd64 2.4.29-1ubuntu4.12 [1071 kB]
Get:32 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 apache2-utils amd64 2.4.29-1ubuntu4.12 [83.5 kB]
Get:33 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 apache2-data all 2.4.29-1ubuntu4.12 [160 kB]
Get:34 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 apache2 amd64 2.4.29-1ubuntu4.12 [95.1 kB]
Get:35 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libmagic-mgc amd64 1:5.32-2ubuntu0.3 [184 kB]
Get:36 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libmagic1 amd64 1:5.32-2ubuntu0.3 [68.7 kB]
Get:37 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 file amd64 1:5.32-2ubuntu0.3 [22.1 kB]
Get:38 http://archive.ubuntu.com/ubuntu bionic/main amd64 netbase all 5.4 [12.7 kB]
Get:39 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 openssl amd64 1.1.1-1ubuntu2.1~18.04.5 [613 kB]
Get:40 http://archive.ubuntu.com/ubuntu bionic/main amd64 xz-utils amd64 5.2.2-1.3 [83.8 kB]
Get:41 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 libsasl2-modules amd64 2.1.27~101-g0780600+dfsg-3ubuntu2.1 [48.8 kB]
Get:42 http://archive.ubuntu.com/ubuntu bionic/main amd64 ssl-cert all 1.0.39 [17.0 kB]
Fetched 21.0 MB in 1s (15.5 MB/s)
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Setting up libssl1.1:amd64 (1.1.1-1ubuntu2.1~18.04.5) ...
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
Setting up xz-utils (5.2.2-1.3) ...
update-alternatives: using /usr/bin/xz to provide /usr/bin/lzma (lzma) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/man1/lzma.1.gz because associated file /usr/share/man/man1/xz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/unlzma.1.gz because associated file /usr/share/man/man1/unxz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzcat.1.gz because associated file /usr/share/man/man1/xzcat.1.gz (of link group lzma) doesn't exist
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update-alternatives: warning: skip creation of /usr/share/man/man1/lzfgrep.1.gz because associated file /usr/share/man/man1/xzfgrep.1.gz (of link group lzma) doesn't exist
Setting up libaprutil1:amd64 (1.6.1-2) ...
Setting up libheimbase1-heimdal:amd64 (7.5.0+dfsg-1) ...
Setting up openssl (1.1.1-1ubuntu2.1~18.04.5) ...
Setting up libsqlite3-0:amd64 (3.22.0-1ubuntu0.2) ...
Setting up liblua5.2-0:amd64 (5.2.4-1.1build1) ...
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Setting up libsasl2-modules:amd64 (2.1.27~101-g0780600+dfsg-3ubuntu2.1) ...
Setting up netbase (5.4) ...
Setting up libwind0-heimdal:amd64 (7.5.0+dfsg-1) ...
Setting up libaprutil1-dbd-sqlite3:amd64 (1.6.1-2) ...
Setting up apache2-utils (2.4.29-1ubuntu4.12) ...
Setting up libasn1-8-heimdal:amd64 (7.5.0+dfsg-1) ...
Setting up libhcrypto4-heimdal:amd64 (7.5.0+dfsg-1) ...
Setting up ssl-cert (1.0.39) ...
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
Setting up file (1:5.32-2ubuntu0.3) ...
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Setting up libperl5.26:amd64 (5.26.1-6ubuntu0.3) ...
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Setting up perl (5.26.1-6ubuntu0.3) ...
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Setting up libldap-2.4-2:amd64 (2.4.45+dfsg-1ubuntu1.4) ...
Setting up libaprutil1-ldap:amd64 (1.6.1-2) ...
Setting up apache2-bin (2.4.29-1ubuntu4.12) ...
Setting up apache2 (2.4.29-1ubuntu4.12) ...
Enabling module mpm_event.
Enabling module authz_core.
Enabling module authz_host.
Enabling module authn_core.
Enabling module auth_basic.
Enabling module access_compat.
Enabling module authn_file.
Enabling module authz_user.
Enabling module alias.
Enabling module dir.
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Enabling module setenvif.
Enabling module filter.
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Enabling module reqtimeout.
Enabling conf charset.
Enabling conf localized-error-pages.
Enabling conf other-vhosts-access-log.
Enabling conf security.
Enabling conf serve-cgi-bin.
Enabling site 000-default.
invoke-rc.d: could not determine current runlevel
invoke-rc.d: policy-rc.d denied execution of start.
Processing triggers for libc-bin (2.27-3ubuntu1) ...
root@08534d150381:/# /etc/init.d/apache2 start
* Starting Apache httpd web server apache2 AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.3. Set the 'ServerName' directive globally to suppress this message
*
root@08534d150381:/#
Como podemos ver, la salida de los comandos en la imagen ubuntu, es infinitamente más detallada, para bien o para mal. Además, intala muchas cosas que en la mayoría de los casos ni las utilizaremos.
Si lanzamos un docker system df -v vemos lo siguiente:
REPOSITORY TAG IMAGE ID CREATED SIZE SHARED SIZE UNIQUE SIZE CONTAINERS
ubuntu latest 72300a873c2c 2 weeks ago 64.21MB 0B 64.21MB 1
alpine latest e7d92cdc71fe 7 weeks ago 5.591MB 0B 5.591MB 1
Containers space usage:
CONTAINER ID IMAGE COMMAND LOCAL VOLUMES SIZE CREATED STATUS NAMES
08534d150381 ubuntu "bash" 0 125MB 3 minutes ago Up 3 minutes unruffled_hellman
a79f841722c5 alpine "sh" 0 6.22MB 34 minutes ago Up 34 minutes lucid_wiles
La imagen ubuntu, ocupa 64 MB, y el contenedor, después de hacer un apt update y un apt install apache2 ocupa 125 MB
Por otro lado, la imagen alpine ocupa 5.5 MB, y despues de hacer un apk update y un apk add apache2 tan solo ocupa 6.22 MB
Conclusión:
Es un hecho que cuantos más programas, más posibilidades de bugs
También que tener en cuenta lo siguiente:
Si nuestra aplicación es grande y ocupa por ejemplo 1GB, es posible que la diferencia de tamaño entre las imágenes no sea muy relevante. Pero si estamos pensando en un sistema basado en microservicios, con aplicaciones pequeñas, esta diferencia de tamaño es enorme.
Por poner un ejemplo más concreto, la última api que hice, que procesa las peticiones del buscador de este blog, y las manda a un solr, ocupa 12 MB.
-rwxr-xr-x 1 athos athos 12M mar 8 13:55 api
Si hacemos los cálculos, con una imagen alpine, el total sería de 17MB, en cambio con la imagen ubuntu ocuparía 76 MB.
Sigue sin ser, hoy en día, una diferencia muy grande, pero tambien hay que tener en cuenta, que con la alpine, la api funciona exactemente igual, se descarga más rápido, y es probable que tenga menos fallos de seguridad.
Os animo a utilizar imágenes alpine cuando lo veáis conveniente