As we all know containers are ephemeral in nature and it does not persist the data. If container is removed the data is gone along with it. So per fix this issue, we can attached a persistent storage with container. To do the same, we configure a folder on host file system to be attached to container for persistent storage.
we will start will creating a folder on host system.
We will also need to take care of SElinux labeling, so we will setup a rule for '/var/local/mysql' folder and anything underneath. So once rule is set run restorecon to change label.
After the selinux labeling is setup we will also have to take care of file system permission, so that container to write on the filesystem of host. Since we are taking example of Mysql process, we will change ownership to mysql uid and gid for the folder.
Now we are all set to run a container. So we will have to pull the image. You might need to login to the registry if needed.
Now we have the image fetached, lets run the container with the storage mount of '/var/local/mysql' folder of host to container folder of '/var/lib/mysql/data'.
-d = Running container in background
-v = Bind a volume
-e = Environmental variable
After running the container, you will find bunch of files created underneath the /var/local/mysql folder. Also you might notice that the files are owned by Mysql uid and gid.
Now, we will access the shell of the container to access the mysql process.
We can access the database we created called 'projectmanhattan' and we will create the database with a table called 'newyork'.
One table is created under the database, lets populate it with some data to test the data persistence of storage.
Now we will delete the old container named 'mydb1' and create another container named 'mydb2' with same properties and mounting the same volume to verify if data persisted or not. We can see that data still exists even after deleting the initial container.
Conclusion:
We are able to persist the data if we mount the host file system storage in the container.
We can install Docker containers in two different ways, One is to install the same with the yum package manager directly or second method is we can use curl with the get.docker.com site. We will be using yum this time.
1. Log into our machine as a user with sudo or root privileges.
2. Make sure our server existing yum packages are up-to-date.
# yum update
3. Add the yum repo:
# vim /etc/yum.repos.d/docker.repo
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg
Install the Docker package.
# yum install docker-engine
After, Docker package has been installed, start the daemon, check its status and enable it system wide using the below commands:
Verify docker is installed correctly by running a test image in a container.
# docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from hello-world
a8219747be10: Pull complete
91c95931e552: Already exists
hello-world:latest: The image you are pulling has been verified. Important: image verification is a tech preview feature and should not be relied on to provide security.
Digest: sha256:aa03e5d0d5553b4c3473e89c8619cf79df368babd1.7.1cf5daeb82aab55838d
Status: Downloaded newer image for hello-world:latest
Hello from Docker.
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
(Assuming it was not already locally available.)
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.
Now, you can run a few basic Docker commands to get info about Docker:
For system-wide information on Docker
# docker info
# docker version
4. In order to start and run a Docker container, first an image must be downloaded from Docker Hub on your host. Docker Hub offers a great deal of free images from its repositories.
To search for a Docker image, Ubuntu for instance, issue the following command:
# docker search ubuntu
5. We want to run Ubuntu, So download it locally by running the below command
# docker pull ubuntu
6. To list all the available Docker images on your host issue the following command:
# docker images
7. In order to create and run a container, you need to run a command into a downloaded image, in this caseUbuntu, so a basic command would be to display the distribution version file inside the container using cat command, as in the following example:
# docker run ubuntu cat /etc/issue
8. To run one of the containers again with the command that was executed to create it, first you must get the container ID (or the name automatically generated by Docker) by issuing the below command, which displays a list of the running and stopped (non-running) containers:
# docker ps -l
9. Once the container ID has been obtained, you can start the container again with the command that was used to create it, by issuing the following command:
# docker start <Container ID>
10. In order to interactively connect into a container shell session, and run commands as you do on any other Linux session, issue the following command:
# docker run -it ubuntu bash
11. To quit and return to host from the running container session you must type exit command. The exit command terminates all the container processes and stops it.
# exit
12. To reconnect to the running container you need the container ID or name. Issue docker ps command to get the ID or name and, then, run docker attach command by specifying container ID or name, as illustrated in the image above:
# docker attach <container id>
Install Apache Web server in Docker container
Once I start the new docker container as describe earlier, I will start two new containers for my Apache and Mysql deployment
Once you are in the Ubuntu docker container, install the apache packages
# apt-get update && apt-get install apache2
Now its time to start the service,
# /etc/init.d/apache2 start
To verify if the server is running, try using links command. (We might need to install it if thats not available.
# apt-get install links (if links command is not installed)
# links http://127.0.0.1
To store the current state of the Docker containers, we need to commit them, so that they start with your configuration next time when you start them by 'exit' command.
# docker commit <container ID> yogesh/apache
Install MySQL server in Docker container
In other TAB, we can start one more Docker container for Mysql server
# apt-get update
# apt-get install mysql-server
(Type password when asked for Mysql database password)
After mysql is installed, start the service:
# /etc/init.d/mysql start
Try and test it out:
# mysql -u root -p
(Type password)
> show databases;
(Displays all default databases)
>exit
(To exit out of server)
Default Logs for mysql are saved in /var/log/mysql/error.log
To store the current state of the Docker containers, we need to commit them, so that they start with your configuration next time when you start them after the 'exit'.
# docker commit <container ID> yogesh/mysql
You can view the complete procedure in below video:
Icinga is a modern open source monitoring tool that originated from a Nagios itself. The ICINGA tool is not much different from Nagios as they use the similar plugins as the Nagios uses but the major differences could be seen in Web UI and interface.
We will be going through entire deployment and installation process of Icinga Monitoring Tool for RHEL 7, using repoforge(Earlier known as RPMforge), EPEL & Icigna repositories for Apache and Nagios plugins which needs to be installed in the system.
1. Before proceeding with Icinga installation we need to configure RepoForge & ICINGA repositories on the sever by using below command
2. The next step is to try to install Icinga web interface provided by icinga-gui package. Earlier CentOS/RHEL 7 has some issues with the package, but its fixed in latest version of CentOS/RHEL releases
# yum install icinga-gui
3. After RepoForge & icinga repositories had been added on your system, start with Icinga deployment
# yum install icinga icinga-doc
4. Install Apache development packages:
# yum install httpd-devel
4. As presented on this article introduction, your system needs to have Apache HTTP server and PHP installed in order to be able to run Icinga Web Interface.
After you finished the above steps, a new configuration file should be now present on Apache conf.d path named icinga.conf. In order to be able to access Icinga from a remote location from browser, open this configuration file and replace all its content with the following configurations.
# vim /etc/httpd/conf.d/icinga.conf
Make sure you replace all file content with the following.
ScriptAlias /icinga/cgi-bin "/usr/lib64/icinga/cgi"
<Directory "/usr/lib64/icinga/cgi">
# SSLRequireSSL
Options ExecCGI
AllowOverride None
AuthName "Icinga Access"
AuthType Basic
AuthUserFile /etc/icinga/passwd
<IfModule mod_authz_core.c>
# Apache 2.4
<RequireAll>
Require all granted
# Require local
Require valid-user
</RequireAll>
</IfModule>
<IfModule !mod_authz_core.c>
# Apache 2.2
Order allow,deny
Allow from all
# Order deny,allow
# Deny from all
# Allow from 127.0.0.1
Require valid-user
</IfModule>
</Directory>
Alias /icinga "/usr/share/icinga/"
<Directory "/usr/share/icinga/">
# SSLRequireSSL
Options None
AllowOverride All
AuthName "Icinga Access"
AuthType Basic
AuthUserFile /etc/icinga/passwd
<IfModule mod_authz_core.c>
# Apache 2.4
<RequireAll>
Require all granted
# Require local
Require valid-user
</RequireAll>
</IfModule>
<IfModule !mod_authz_core.c>
# Apache 2.2
Order allow,deny
Allow from all
# Order deny,allow
# Deny from all
# Allow from 127.0.0.1
Require valid-user
</IfModule>
</Directory>
5. After you have edited Icinga httpd configuration file, add Apache system user to Icinga system group and use the following system permissions on next system paths.
6. Before starting Icinga system process and Apache server, make sure you also disable SELinux security mechanism by running 'setenforce 0' command and make the changes permanent by editing /etc/selinux/config file, changing SELINUX context from enforcing to disabled.
# nano /etc/selinux/config
Modify SELINUX directive to look like this.
SELINUX=disabled
You can also use 'getenforce' command to view SELinux status.
7. As the last step before starting Icinga process and web interface, as a security measure you can now modify Icinga Admin password by running the following command, and then start both processes.
8. In order to start monitoring public external services on hosts with Icinga, such as HTTP, IMAP, POP3, SSH, DNS, ICMP ping and many others services accessible from internet or LAN you need to install Nagios Plugins package provided by EPEL Repositories.
9. To login on Icinga Web Interface, open a browser and point it to the URL http://Amazon_EC2_hostname/icinga/. Use icingaadmin as username and the password you chose earlier and you can now see your localhost system status.
That is the process of installing and configuring Icinga server on Red Hat enterprise linux 7.
Checkout below video for more practical representation:
Monday, May 23, 2016
How to work with Ansible (Automation tool) on CentOS 7
Ansible is free tool to automation tool for Linux hosts. Its useful for the environment where you have lots of linux hosts/servers to manage and maintain. Lets get started with it, I have tested the below mentioned steps on CentOS 7: First of all, we are going to need epel on CentOS to install ansible:
[root@vm2 ~]# uname -r
3.10.0-123.el7.x86_64
[root@vm2 ~]# cat /etc/redhat-release CentOS Linux release 7.0.1406 (Core)
[root@vm2 ~]# yum install epel-release Now after installing epel, lets install ansible: [root@vm2 ~]# yum install ansible
Now, ansible works on ssh keys. So just generate one if you don't have it.
[root@vm2 ~]# ssh-keygen <You can have a secure password, or just keep it blank also should work> Your identification has been saved in /root/.ssh/id_rsa. Your public key has been saved in /root/.ssh/id_rsa.pub.
Yeah, So Now you are able to fetch these information in single command.
[root@vm2 ~]# ansible -m command -a 'grep CPU /proc/cpuinfo' 'test-servers' 192.168.0.81 | SUCCESS | rc=0 >> model name : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz 192.168.1.222 | SUCCESS | rc=0 >> model name : Intel(R) Core(TM) i3-3240 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-3240 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-3240 CPU @ 3.40GHz model name : Intel(R) Core(TM) i3-3240 CPU @ 3.40GHz
[root@vm2 ~]# ansible -m command -a 'free -m' 'test-servers' 192.168.1.222 | SUCCESS | rc=0 >> total used free shared buffers cached Mem: 7693 5845 1847 187 7 449 -/+ buffers/cache: 5388 2304 Swap: 7999 684 7315 192.168.0.81 | SUCCESS | rc=0 >> total used free shared buff/cache available Mem: 11726 6426 390 393 4909 4568 Swap: 16383 130 16253
[root@vm2 ~]# ansible -m command -a 'fdisk -l /dev/sda' 'test-servers' 192.168.0.81 | SUCCESS | rc=0 >> Disk /dev/sda: 500.1 GB, 500107862016 bytes, 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x0000f988 Device Boot Start End Blocks Id System /dev/sda1 * 2048 1230847 614400 83 Linux /dev/sda2 1230848 525518847 262144000 83 Linux /dev/sda3 525518848 559073279 16777216 82 Linux swap / Solaris /dev/sda4 559073280 976773167 208849944 5 Extended /dev/sda5 559075328 976773167 208848920 83 Linux 192.168.1.222 | SUCCESS | rc=0 >> Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xa34fa34f Device Boot Start End Blocks Id System /dev/sda1 * 1 32 256000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 32 7681 61440000 83 Linux /dev/sda3 7681 8701 8192000 82 Linux swap / Solaris /dev/sda4 8701 60802 418497560 5 Extended /dev/sda5 8701 60802 418496512 83 Linux
Awesome. You can Also Create/Delete user accounts:
When you install postfix for the first time, system will ask you for the smtp domain name and smtp type. Select "Internet Site" and "smtp.yourdomain.com" where ever applicable. (Where 'yourdomain.com' is your working domain name)
Now lets start configuring SMTP in postfix.
sudo vim /etc/postfix/main.cf
(Edit configuration file, so that it looks like this..)
Lets make sure postfix can read this file and not everyone else:
sudo chmod 400 /etc/postfix/sasl_passwd
sudo postmap /etc/postfix/sasl_passwd
Lets use the certificate for the authentication:
cat /etc/ssl/certs/Thawte_Premium_Server_CA.pem | sudo tee -a /etc/postfix/cacert.pem
and finally lets restart the postfix service:
/etc/init.d/postfix reload
Now let's test our configuration if its working or not:
echo "Test email from Postfix" | mail -s "Test Postfix" USERNAME@gmail.com
Verify is the mail is sent:
tail -f /var/log/mail.log
If required we can also add your gmail account in aliases:
vim /etc/aliases
root: GMAILADDRESS@gmail.com
(save & exit)
newaliases
Thanks for the visit
:)
Monday, August 10, 2015
Working with apt-get and dpkg package manager tools of 'Debian'
First of all we are going to work with Apt-get package manager. For those who are already familiar with Yum of Red Hat based distros may find this quite identical tool. Apt-get pulls and installs packages from the online repository to ease your pain to find, download and install packages and its dependency manually. You have to be root using for the following hands-on, Let's get started: root@yogeshkk21:~# apt-get update This command pulls package information from repository server and caches the same locally root@yogeshkk21:~# apt-cache search nginx We can search for a specific package in the entire cache using this command
root@yogeshkk21:~# apt-get install nginx This command is to install a package root@yogeshkk21:~#which nginx To verify nginx is installed
root@yogeshkk21:~#apt-cache search apache2 Let's search for Apache2 package as well root@yogeshkk21:~#apt-get install apache2 And Install it same as nginx root@yogeshkk21:~#apt-get remove ngnix Now, let's learn How to remove it root@yogeshkk21:~#apt-get remove --purge nginx apt-get remove only removes the binary, but keeps associated library and configuration files. So to remove everything, use purge. root@yogeshkk21:~#apt-get autoremove This command removes unnecessary packages alongside the removed package root@yogeshkk21:~#which ngnix Let's verify root@yogeshkk21:~#apt-get remove apache2 ; apt-get autoremove apache2 This removed apache2 package along with unnecessary packages of it root@yogeshkk21:~#which apache2 Let's verify again root@yogeshkk21:~#apt-get install apache2 Let us install apache2 package again root@yogeshkk21:~#apt-get upgrade This command allows you to upgrade any packages required for apache2 root@yogeshkk21:~#apt-get dist-upgrade This command allows you to upgrade distribution kernel if available Now if we talk about dpkg package manager, it's the little bit different from the apt-get. This does not pull the dependencies automatically like apt-get does. Let's see: root@yogeshkk21:~#wget https://www.dropbox.com/download?dl=packages/ubuntu/dropbox_2015.02.12_amd64.deb Let's try to install Dropbox application on our Ubuntu 12.04 distro. root@yogeshkk21:~#mv download\?dl\=packages%2Fubuntu%2Fdropbox_2015.02.12_amd64.deb dropbox.deb Let's rename this downloaded file to something more simple. root@yogeshkk21:~#dpkg -i dropbox.deb To install the Deb file, use -i option. Now you will see that lots of dependency errors are been thrown at you. Its simply because, dpkg can't pull all those dependency for you. So, what now? Should I download and install them manually? No, there is a way out. root@yogeshkk21:~#apt-get update Let's update our cache once again root@yogeshkk21:~#apt-get -f upgrade And this command will do the job for us. It automatically pulls all the required library packages along with other dependencies. Nice, right? root@yogeshkk21:~#dpkg -i dropbox.deb Now, let's try that deb file again for installation. And you will notice, it gets installed! :) root@yogeshkk21:~#which dropbox Let's verify! Worked well. root@yogeshkk21:~#dpkg --get-selections Now let's also find out, how can we list all installed packages. This command will do the magic for us. root@yogeshkk21:~#dpkg --get-selections |grep -i dropbox We can find specific package name from the output using grep. root@yogeshkk21:~#dpkg --remove dropbox
Just like apt-get we have remove command as well in dpkg and it removes all binary for us. root@yogeshkk21:~#dpkg --purge dropbox To remove the application completely, using this command. So that's how we can use apt-get and dpkg. HTH ^_^ Above command is tested and worked on: root@yogeshkk21:~# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 12.04.5 LTS Release: 12.04 Codename: precise
