After showing the creation of an exemplary Docker container in the first part, this part of the article series now focuses on working with containers.<\/p>\n\n\n\n
Creating a Docker container is done using the build command. For this, we must be in the Dockerfile folder, otherwise the location of the Dockerfile must also be specified.<\/p>\n\n\n\n
docker build -t opensuse-tomcat .<\/pre>\n\n\n\nDocker now creates a corresponding Docker image named opensuse-tomcat. This now serves as a template for the containers we want to use (runtime environment(s)).<\/p>\n\n\n\n
If errors occur, e.g. the files to be added via ADD cannot be found, this is displayed in the form of corresponding messages on the console. The following is an example of a missing file:<\/p>\n\n\n\n
Step 13\/22 : ADD .\/webapp.war \/opt\/tomcat\/webapp\/\nADD failed: no source files were specified<\/pre>\n\n\n\n<\/p>\n\n\n\n
Images<\/h4>\n\n\n\n
If we now want to know which usable images already exist on the host system, enter the following:<\/p>\n\n\n\n
docker images<\/pre>\n\n\n\nAs feedback we get<\/p>\n\n\n\n
REPOSITORY TAG IMAGE ID CREATED SIZE\nopensuse-tomcat latest 662c7e16ad72 2 days ago 378MB\ndebian-tomcat latest deeb279b66c2 3 days ago 319MB\nopensuse\/leap 15.2 9c0b2c564878 10 days ago 105MB\nopensuse\/leap 15.1 b1ee6ac1cd81 11 days ago 106MB<\/pre>\n\n\n\n<\/p>\n\n\n\n
Run<\/h4>\n\n\n\n
The start of a new container based on an image is done with run. Additionally, a port mapping can be specified with -p. If there are several ports, the p parameter is simply repeated<\/p>\n\n\n\n
docker run -p 8080:8080 -p 8443:8443 opensuse-tomcat<\/pre>\n\n\n\n<\/p>\n\n\n\n
Name<\/h4>\n\n\n\n
Docker assigns randomly generated names to the running instances by default. If the container is to be specifically addressed by a name, it is possible to assign a name to it at startup using -name <name><\/p>\n\n\n\n
docker run -p 8080:8080 -p 8009:8009 -name tomcat01 opensuse-tomcat <\/pre>\n\n\n\n<\/p>\n\n\n\n
Entrypoint<\/h4>\n\n\n\n
In the first part of this article series, we defined a so-called entrypoint in the Dockerfile. This is executed when the container is started. However, if you do not want to have this hardwired or overwrite it, the entrypoint parameter is available for this purpose. The associated argument defines what is to be executed at the end of the startup process. In this case we execute the shutdown.sh script of the Tomcat. The additional parameter rm specifies that the container is also removed after it has been shut down.<\/p>\n\n\n\n
docker run --rm --entrypoint=\/opt\/tomcat\/bin\/shutdown.sh -p 8080:8080 -p 8009:8009 opensuse-tomcat<\/pre>\n\n\n\n<\/p>\n\n\n\n
Exec<\/h4>\n\n\n\n
If you want to run the above shell script in a running container (named tomcat01) exec is used, which I would prefer for terminating a running Tomcat.<\/p>\n\n\n\n
docker exec tomcat01 \/opt\/tomcat\/bin\/shutdown.sh<\/pre>\n\n\n\n<\/p>\n\n\n\n
Mount (v)<\/h4>\n\n\n\n
For the operation of a Tomcat, the log files are a helpful source, e.g. for troubleshooting. Here it makes sense that Tomcat writes to a directory specific to its instance. This can be specified externally with the v parameter. For this the external path and its mountpoint within the container is specified.<\/p>\n\n\n\n
docker run -it --rm -p 8080:8080 -p 8009:8009 -v D:\\docker\\tomcat01\\log:\/opt\/tomcat\/logs --name tomcat01 opensuse-tomcat<\/pre>\n\n\n\nEach instance can thus be given its own log directory at startup.<\/p>\n\n\n\n
<\/p>\n\n\n\n
Environment variables (env-file) and hostname (h)<\/h4>\n\n\n\n
If I now want to set additional environment variables from outside within the container, which e.g. the web application can access in order to adapt specifically depending on e.g. a stage information, then this and further environment variables and values can be specified by means of env-file and so-called properties files when starting the container. By means of the given entrypoint the defined environment variables are output in this example.<\/p>\n\n\n\n
docker run --entrypoint=\/usr\/bin\/env --env-file env-vars.properties -h testhost123 opensuse-tomcat<\/pre>\n\n\n\nThe following is an example of a Propierties file. The name of this file can be assigned arbitrarily and does not have to follow any defaults.<\/p>\n\n\n\n
var1=1111
var2=2222<\/pre>\n\n\n\nBy calling \/usr\/bin\/env the defined environment variables are now output:<\/p>\n\n\n\n
HOSTNAME=testhost123
var1=1111
var2=2222
HOME=\/root<\/pre>\n\n\n\nThe output hostname was not part of the properties file, it was passed by means of the h parameter when the container was started.<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
After showing the creation of an exemplary Docker container in the first part, this part of the article series now focuses on working with containers.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,3,10],"tags":[14,16,15],"class_list":["post-228","post","type-post","status-publish","format-standard","hentry","category-allgemein","category-linux","category-netzwerk","tag-docker","tag-linux","tag-tomcat"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/posts\/228","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/comments?post=228"}],"version-history":[{"count":14,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/posts\/228\/revisions"}],"predecessor-version":[{"id":388,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/posts\/228\/revisions\/388"}],"wp:attachment":[{"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/media?parent=228"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/categories?post=228"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rothamel.com\/index.php\/wp-json\/wp\/v2\/tags?post=228"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}