{"id":26168,"date":"2015-09-14T12:36:17","date_gmt":"2015-09-14T07:06:17","guid":{"rendered":"http:\/\/www.tothenew.com\/blog\/?p=26168"},"modified":"2016-01-19T13:32:30","modified_gmt":"2016-01-19T08:02:30","slug":"docker-containers-and-aws-auto-scaling-hand-in-hand","status":"publish","type":"post","link":"https:\/\/www.tothenew.com\/blog\/docker-containers-and-aws-auto-scaling-hand-in-hand\/","title":{"rendered":"Docker containers and AWS Auto-scaling – Hand in Hand"},"content":{"rendered":"

In my previous blog<\/a>, I talked about setting up sendmail inside a Docker container.\u00a0In this blog, we will talk about how to make your Docker<\/a> containers come up during Auto-scaling of AWS servers, start, and use a service like sendmail inside them. You can make changes to scripts based on your use-case. I just want to make the logic clear.<\/p>\n

\"cicd-with-docker-on-aws-1-638\"<\/strong><\/h3>\n

<\/h3>\n


\nUse-case\u00a0<\/strong><\/p>\n

I had a PHP application running inside my Docker container (CentOS 7 based), being served by httpd (Apache2). This was single container running on a host machine. A use-case arose when I thought of what would happen when the traffic to my website increased or the CPU utilization went high etc. . I would have to scale my containers i.e. launch a new server and run a container inside that. Also, what I needed to do is keep the containers isolated & check whether the container has come up in auto-scaling or not. So, that is what the blog is about.\u00a0So, I have made a script which you can add to user data in Launch Configuration.<\/p>\n

Prerequisites\u00a0<\/strong><\/h3>\n

What I will assume is that \u00a0you already have a Docker container running (CentOS 7 based), and it is serving some PHP application through httpd.
\nAlso, what more you need is :-<\/p>\n

    \n
  1. An Auto-scaling group & Launch Configuration in your AWS account.<\/li>\n
  2. Your host machine’s AMI added to the Launch Configuration.<\/li>\n
  3. Latest image of your running container committed to Docker Hub or you may locally commit the container image & create an AMI from that and add to Launch Configuration group.<\/li>\n
  4. Host machine may be Amazon Linux or CentOS\/RedHat. ( Even Ubuntu, but commands may slightly differ)<\/li>\n
  5. sendmail service installed & running on host machine. (This will be used to send an email when Docker container comes up)<\/li>\n<\/ol>\n

    How to implement it<\/h3>\n

    Explanation<\/strong> : Lets talk about the scripts. As we know every time a new container starts the entry in \/etc\/hosts<\/strong> changes to default with the new container ID. As sendmail requires a domain name to work, we will be using 2 scripts for sendmail about which we talked about in the previous blog, first being dockerscriptetchosts.sh<\/strong> and the other being\u00a0startsendmail.sh<\/strong>.\u00a0Let us go through them one by one before we come to our main script autodeploy.sh<\/strong><\/p>\n

    So, the first script for sendmail is\u00a0dockerscriptetchosts.sh<\/strong><\/p>\n

    #!\/bin\/bash\r\n\r\nline=$(head -n 1 \/etc\/hosts) \r\nline2=$(echo $line | awk '{print $2}')\r\n\r\necho \"$line $line2.localdomain\" >> \/etc\/hosts<\/pre>\n
    The above script has already been added to the image using ADD in Dockerfile. It makes the necessary entry to \/etc\/hosts of the Docker container which are as follows :-<\/p>\n
    container_IP container_id container_id.localdomain
    \n<\/code><\/p>\n
    Next script is startsendmail.sh.<\/strong><\/p>\n
    #!\/bin\/bash\r\nsudo docker exec -itd $1 bash \/home\/dockerscriptetchosts.sh\r\nsudo docker exec -itd $1 \/etc\/init.d\/sendmail start\r\nsudo docker exec -itd $1 \/usr\/sbin\/httpd -k restart\r\n<\/pre>\n
    This script is present on the host machine & takes one parameter input (container_id<\/strong>) to execute which we will pass in the main script. It firstly runs docker exec<\/strong> command which in turn runs the command bash \/home\/dockerscriptetchosts.sh<\/strong>\u00a0inside the Docker container and in turn the next commands. The last command restarts httpd.<\/p>\n
    The main script autodeploy.sh<\/strong> is below. Just go through it and I will explain the script just after that. You will need to put this bash script in the user-data<\/strong>.<\/p>\n
    [js]#!\/bin\/bash
    \nsudo docker pull ranvijayj\/prod:latest #this is if you want to pull from Docker Hub<\/p>\n
    container_id=$(docker run -idt -p 80:80 –restart="always" -v \/mnt\/code:\/opt\/code prod:latest)<\/p>\n
    #check whether container is running or not<\/p>\n
    sleep 5<\/p>\n
    if [ `docker inspect -f {{.State.Running}} $container_id` == "true" ]; then<\/p>\n
     echo "Container has restarted .. Volume mounted" | sendmail -s " Container has come up in autoscaling" ranvijay.jamwal@tothenew.com
    \n sleep 20
    \n http_status=$(curl -Is localhost:80 | head -n 1 | awk ‘{ print $2}’)<\/p>\n
     if [ $http_status == 200 ]; then<\/p>\n
     echo "Container is SERVING the website" | sendmail -s " Container is serving the website" ranvijay.jamwal@tothenew.com<\/p>\n
     #once the container has started we need to start the sendmail service
    \n #startsendmail can be present in any directory of AMI
    \n bash \/home\/ec2-user\/startsendmail.sh<\/p>\n
     else
    \n echo "Container has FAILED to serve the website.. http_status= $http_status" | sendmail -s " Container is NOT SERVING at port 80" ranvijay.jamwal@tothenew.com
    \n fi<\/p>\n
    else
    \n echo "Container has not restarted\/started" | sendmail -s " Container has failed to come up in autoscaling &amp; is NOT serving the website" ranvijay.jamwal@tothenew.com<\/p>\n
    fi [\/js]<\/p>\n
     <\/p>\n
    So, what the script is doing, is the following & we will understand it line by line :-<\/p>\n
      \n
    1. Using the Docker image we have defined it launches a container in detached mode<\/li>\n
    2. It also exposes port 80 to the outside world, mounts directory \/mnt\/code<\/strong> from host machine to \/opt\/code<\/strong> using -v<\/strong> switch, \u00a0sets the variable —restart<\/strong> to “always” for the container & the container ID is stored in the variable container_id.\u00a0<\/strong>Inside \/mnt\/code is your PHP code. The httpd service will start on its own as I already added a CMD<\/strong> via Dockerfile<\/strong> i.e.
      \nENTRYPOINT [“\/usr\/sbin\/httpd”]<\/strong>
      \n CMD [“-D”,”FOREGROUND”,”-k”,”start”]<\/strong>
      \nor you can use Nginx etc. You might have done this already<\/li>\n
    3. Sleep for 5 seconds<\/li>\n
    4. The first if statement checks if the container has started & then sends an email to the specified email address according to the result. We are checking that using the command\u00a0docker inspect -f {{.State.Running}} $container_id` <\/strong>& it should return a string “true”. Add a sleep of 20 seconds<\/li>\n
    5. Next is checking if the container is serving the website on 80 port. For that we curl localhost:80. If it returns 200 then the website is working else it is not serving the website<\/li>\n
    6. Now, since that is working, next is getting sendmail up & running. For that execute the dockersendmail.sh script. This will work as we discussed above.<\/li>\n<\/ol>\n
      Now, everything should be working fine & your docker container will start when your servers auto-scale.<\/p>\n","protected":false},"excerpt":{"rendered":"
      In my previous blog, I talked about setting up sendmail inside a Docker container.\u00a0In this blog, we will talk about how to make your Docker containers come up during Auto-scaling of AWS servers, start, and use a service like sendmail inside them. You can make changes to scripts based on your use-case. I just want […]<\/p>\n","protected":false},"author":174,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"iawp_total_views":16,"footnotes":""},"categories":[1174,2348],"tags":[248,1257,2366,1883,2335,2250,2249,2336],"class_list":["post-26168","post","type-post","status-publish","format-standard","hentry","category-aws-2","category-devops-technology","tag-aws","tag-aws-auto-scaling","tag-aws-devops","tag-docker","tag-docker-autoscaling","tag-docker-centos","tag-docker-exec","tag-docker-sendmail"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t