You noticed that some ServerTemplates published by RightScale use v4 RightImages while all newer ServerTemplates published by RightScale use v5 RightImages. You want to understand the differences between these two versions of RightImages and why it makes sense to use v5 RighImages for all future Server development or understand why you should strongly consider migrating any existing Deployments built on v4 RightImages to use newer ServerTemplates built on v5 RightImages.
The first thing you should understand is that all functionality that is available in v4 RightImages is supported in v5 RightImages. For example, although one of the main benefits of v5 RightImages is its support for Chef Recipes, you can still run any RightScripts on v5 Servers. So, if you migrate to use v5 RightImages, you will not lose any functionality that you enjoyed with v4 RightImages. It's strongly recommended that you migrate any existing Deployments to use v5 RightImages.
There are several advantages and benefits of using v5 RightImages, which will be discussed in more detail below.
The key differences between v4 and v5 RightImages can be summarized as affecting the following topics:
One of the key differences between v4 and v5 RightImages is that v5 (and later) RightImages install a RightLink agent on the instance that allows RightScale to more efficiently communicate with the instance. A RightLink-enabled RightImage is also required in order to run Chef recipes on an instance. Other software tools like Puppet can be installed and configured on v4 or v5 RightImages.
For instances launched with v4 RightImages, the EC2 SSH Key is used to establish SSH (shell) access to the instance. When you launch an EC2 instance, you must select an EC2 SSH Key that will be used to establish a secure client-server connection with the instance. Therefore, if you want to SSH into the instance from inside the RightScale Dashboard, you must use an SSH Key for which the private key material is available and not missing. The private key material in only sent once when the SSH Key is created. So if you're using an EC2 SSH Key that you created outside the RightScale platform, you will need to manually copy the private key material in the Dashboard for the matching key.
For instances launched with v5 RightImages, RightScale's Managed SSH feature will be used to establish SSH (shell) access to the instance. You can either use the unique SSH Key that RightScale generates for each user or upload your own SSH Key. You will still need to select an EC2 SSH Key in order to launch the instance, however since it's no longer used to establish an SSH console session from the RightScale Dashboard, even if the EC2 SSH Key has missing private key material, you will still be able to SSH into the instance.
The execution of RightScripts is supported on Servers that are launched with v4 or v5 RightImages. However, the manner in which those scripts are run on a Server differs depending on whether it's a v4 or v5 and later RightImage.
For Servers that are launched with v4 RightImages (e.g. RightImage CentOS_5.2_i386_v4.2.5), RightScale uses the EC2 SSH Key in order to SSH into an instance over port 22 and run the script(s). Therefore, it's important that RightScale has the private key material for the Server's assigned EC2 SSH Key, otherwise RightScale will not be able to establish a secure client-server connection in order to run the specified RightScripts on the Server. In order to successfully launch a Server in EC2 using a v4 RightImage where the specified boot scripts can be run on the Server, the following cloud resources must be configured properly:
If you launch a Server with an EC2 SSH Key for which RightScale does not have the private key material stored in the RightScale database, the Server will become "stranded in booting" because RightScale will be unable to complete the boot process and run the specified Boot Scripts.
Note: Even though the launched Server is stranded in booting you will continue to be charged by AWS for hourly usage of that instance.
For Servers launched with v5 RightImages, bi-directional communication is used between the RightLink agent on the Server and RightScale's core site for coordinating the execution of scripts on a Server. Instead of using the EC2 SSH Key to SSH into an instance over port 22 and run the script (as with v4 RightImages), a RightLink agent is installed on the instance and is used for communicating with the RightScale platform over a secure connection.
For Servers launched with v4 RightImages, RightScale makes inbound connections to the Server over port 22. Servers were required to have port 22 open so that RightScale would be able to initiate contact with the Server.
For Servers launched with v5 RightImages, there is now bi-directional communication between Servers and RightScale. A Server's Security Group is no longer required to have port 22 open since RightScale no longer makes inbound connections to the running Server. Instead, the RightLink agent on the Server makes an outbound connection to RightScale. However, you will still need to open up port 22 to provide normal SSH access.
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