Nov 2, 2016 - There are two methods for installing Docker on CentOS 7. Build an image from a Dockerfile commit Create a new image from a container's. You can run MySQL (or MariaDB, an open source MySQL-compatible database) on CentOS in a Docker container.However, unless you are running it merely as a temporary test environment, I would recommend against it. Any changes to the database would not be persistent and would be lost if you started another instance of the container.
Build Configure Docker Images with Dockerfile – Part 3Docker images can be automatically build form text files, named Dockerfiles. A Docker file contains step-by-step ordered instructions or commands used to create and configure a Docker image.
Requirements.Basically, a Docker file contains various instructions in order to build and configure a specific container based on your requirements. The following instructions are the most used, some of them being mandatory:. FROM = Mandatory as first instruction in a Docker file. Instructs Docker to pull the base image from which you are building the new image. Use a tag to specify the exact image from which you are building:Ex: FROM ubuntu:14.04. MAINTAINER = Author of the build image. RUN = This instruction can be used on multiple lines and runs any commands after Docker image has been created.
CMD = Run any command when Docker image is started. Use only one CMD instruction in a Dockerfile. ENTRYPOINT = Same as CMD but used as the main command for the image. EXPOSE = Instructs the container to listen on network ports when running.
The container ports are not reachable from the host by default. ENV = Set container environment variables. ADD = Copy resources (files, directories or files from URLs).Step 1: Creating or Writing Dockerfile Repository1. First, let’s create some kind of Dockerfile repositories in order to reuse files in future to create other images.
Make an empty directory somewhere in /var partition where we will create the file with the instructions that will be used to build the newly Docker image. # mkdir -p /var/docker/ubuntu/apache# touch /var/docker/ubuntu/apache/Dockerfile.
Dockerfile RepositoryNow, let’s go through the file instructions:The first line tells us that we are building from an Ubuntu image. If no tag is submitted, say 14:10 for example, the latest image from Docker Hub is used.On the second line we’ve added the name and email of the image creator. Next two RUN lines will be executed in the container when building the image and will install Apache daemon and echo some text into default apache web page.The EXPOSE line will instruct Docker container to listen on port 80, but the port will be not available to outside. The last line instructs the container to run Apache service in foreground after the container is started.3. The last thing we need to do is to start creating the image by issuing the below command, which will locally create a new Docker image named ubuntu-apache based on the Dockerfile created earlier, as shown in this example: # docker build -t ubuntu-apache /var/docker/ubuntu/apache/. Run Docker Container ImageHere, the -d option runs the ubuntu-apache container in background (as a daemon) and the -p option maps the container port 80 to your localhost port 81.
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Outside LAN access to Apache service can be reached through port 81 only.will give you an idea about what ports the host is listening to.After the container has been started, you can also run docker ps command to view the status of the running container.6. The webpage can be displayed on your host from command line using curl utility against your machine IP Address, localhost or docker net interface on port 81. Use line to show network interface IP addresses.
# ip addr List nework interfaces# curl ip-address:81 System Docker IP Address# curl localhost:81 Localhost. Monitor Docker Container Utilization Step 3: Create a System-wide Configuration File for Docker Container11.
On CentOS/RHEL 7 you can create a systemd configuration file and manage the container as you normally do for any other local service.For instance, create a new systemd file named, let’s say, apache-docker.service using the following command: # vi /etc/systemd/system/apache-docker.serviceapache-docker.service file excerpt: UnitDescription=apache containerRequires=docker.serviceAfter=docker.serviceServiceRestart=alwaysExecStart=/usr/bin/docker start -a my-wwwExecStop=/usr/bin/docker stop -t 2 my-wwwInstallWantedBy=local.target12. After you finish editing the file, close it, reload the systemd daemon to reflect changes and start the container by issuing the following commands: # systemctl daemon-reload# systemctl start apache-docker.service# systemctl status apache-docker.serviceThis was just a simple example on what you can do with a simple Dockerfile but you can pre-build some pretty sophisticated applications that you can fire-up in just a matter of seconds with minimal resources and effort. Help, years old instructions.So, i have to hand write a dockerfile, and know what the variables are. So lets just say i followed section 3, the Apache setup, less the mounting external file inside the container, went to follow the instructions to contain it and pump it to AWS/docker service so i need to:“” docker build -t test.” and i get:“unable to prepare context: unable to evaluate symlinks in Dockerfile path: lstat /var/lib/docker/Dockerfile: no such file or directory”You have a “The following instructions are the most used, some of them being mandatory:”so: “FROM” is that the base OS? Or the encapsulated OS?, and what is it referencing that from since its “Mandatory” i cant just do a “ASDF”?
Doing a little looking, that’s the container’s OS variant. So “FROM httpd:2.4”?. “MAINTAINER” is that me? Or the AWS user? Not mandatory?. “RUN” im guessing thats the commands for the container OS?. “CMD” whats this then for?
I thought i did that with RUN. “ENTRYPOINT” “same as CMD” so i run command thrice?. “EXPOSE” is this the same as -P argument? Or different string? I don’t know. “ENV” environment variables, any information on that? What are the things I can variate?
All I know is “HOME /root”. “ADD” so i guess this is null’n’void to me, since CP’ing the files into the container, since I need it self contained.Can I add “ CMD docker cp /media/home/me/Desktop/files.php Container:/var/www/html”?Will that pull files from my desktop when “docker build” command runs? Or do i have to get a container running then do that manually?So I am some what surprised this isn’t populated in a file when you get a docker container to run, you’d think it’ll be part of the docker creation process, base stats with the variables, all the other lovely files are created, why not the basic dockerfile? Why does it have to be hand written? So many mistakes can be made like that.and someone explain to me why docker containers have a underline OS? I thought this system used the base OS and plug dependencies though a “firewall” like feature.Seems like its: BaseOS - Docker - Container OS - Applicationlooks a lot like a VM process: BaseOS - VME - VMOS - Application.
PROBLEM: Any build, with a Dockerfile depending on centos, ubuntu or debian fails to build.ENVIRONMENT: I have a Mac OS X, running VMWare with a guest Ubuntu 14.04, running Docker: mdesales@ubuntu $ sudo docker versionClient version: 1.1.2Client API version: 1.13Go version (client): go1.2.1Git commit (client): d84a070Server version: 1.1.2Server API version: 1.13Go version (server): go1.2.1Git commit (server): d84a070BEHAVIOR: Using 'docker build' fails to download packages. Here's an example of such Dockerfile:,I know that we can run a container with -dns, but this is during the build time.CENTOSFROM centosRUN yum install a b c.UBUNTUFROM ubuntuRUN apt-get install a b cUsers have reported that it might be problems with DNS configuration, others and the configuration has the Google's DNS servers commented out. Step 2: RUN yum install -y curl; yum upgrade -y; yum update -y; yum clean all- Running in 5f11b65c87b8Loaded plugins: fastestmirrorCouldn't resolve host 'mirrorlist.centos.orgStill the problem persisted. So, most users on #docker@Freenode mentioned that it might be a problem with the DNS configuration. So here's my Ubuntu: $ sudo cat /etc/resolv.confnameserver 127.0.1.1search localdomainI tried changing that, same problem.
PROBLEMTalking to some developers at #docker@freenode, the problem was clear to everyone: DNS and the environment. The build works just fine at a regular Internet connection at home.SOLUTION:This problem occurs in an environment that has a private DNS server, or the network blocks the Google's DNS servers.
Even if the docker container can ping 8.8.8.8, the build still needs to have access to the same private DNS server behind your firewall or Data Center.Start the Docker daemon with the -dns switch to point to your private DNS server, just like your host OS is configured. That was found by trial and error.DetailsMy MAC OS X, host OS, had a different DNS configured on my /etc/resolv.conf: mdesales@Marcello-Work (mac) $ cat /etc/resolv.confsearch corp.my-private-company.netnameserver 172.18.20.13nameserver 172.20.100.29My host might be dropping the packets to the Google's IP address 8.8.8.8 while building. I just took those 2 IP addresses and placed under the Ubuntu's docker daemon configuration: mdesales@ubuntu $ cat /etc/default/docker.# Use DOCKEROPTS to modify the daemon startup options.DOCKEROPTS='-dns 172.18.20.13 -dns 172.20.100.29 -dns 8.8.8.8'.The build now works as expected!