I am using EC2 with autoscaling and loadbalancing to host my webapp. To guarantee consistency between the EC2 instances, I only want to allow access to the administration interface from one instance, so all write operations are executed on this instance. The other instaces then periodically download copies of the changed files.
So here's my question:
Can I have a designated "Master" Instance, in my autoscaling group, which is slightly different (runs script for uploading files which were written to)? Of course this Instance should never be shut down, no matter what. All the other "Slave" Instances are indentical an can be created and terminated on demand. Is there some sort of configuration option for this or can I do this with a policy?
My suggestion would be one of two things, either have two autoscaling groups - one for the readonly instances (i.e. the non-master), and then a second ASG for the master instance(s). Even if there is only one master instance at any time, you can still benefit by including it in its own autoscaling group by taking advantage of the ability for the ASG to detect when it has failed, and spin up a single new instance to replace it.
Alternatively, leave the master instance out of the auto-scaling altogether, and just run it as a reserved instances - let the rest of the RO instances scale up and down as necessary.
Related
I have created a cluster to run our test environment on Aws ECS everything seems to work fine including zero downtime deploy, But I realised that when I change instance types on Cloudformation for this cluster it brings all the instances down and my ELB starts to fail because there's no instances running to serve this requests.
The cluster is running using spot instances so my question is there by any chance a way to update instance types for spot instances without having the whole cluster down?
Do you have an AutoScaling group? This would allow you to change the launch template or config to have the new instances type. Then you would set the ASG desired and minimum counts to a higher number. Let the new instance type spin up, go into service in the target group. Then just delete the old instance and set your Auto scaling metrics back to normal.
Without an ASG, you could launch a new instance manually, place that instance in the ECS target group. Confirm that it joins the cluster and is running your service and task. Then delete the old instance.
You might want to break this activity in smaller chunks and do it one by one. You can write small cloudformation template as well because by default if you update the instance type then your instances will be restarted and to avoid zero downtime, you might have to do it one at a time.
However, there are two other ways that I can think of here but both will cost you money.
ASG: Create a new autoscaling group or use the existing one and change the launch configuration.
Blue/Green Deployment: Create the exact set of resources but this time with updated instance type and use Route53's weighted routing policy to control the traffic.
It solely depends upon the requirement, if you can pour money then go with above two approaches otherwise stick with the small deployments.
I just got a word in below link that aws have unprotected instance what is it mean in actualy?
Reference link - https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-instance-termination.html
When using autoscaling you can protect instances from termination during scale in events by selecting them in the Auto Scaling Console and then choosing Instance Protection from the Actions menu.
You might want to do this for several reasons. First, an instance
might be handling a long-running work task, perhaps pulled from an SQS
queue. Protecting the instance from termination will avoid wasted
work. Second, the instance might serve a special purpose within the
group. It could be the master node of a Hadoop cluster or a “canary”
that flags the entire group of instances as up and running.
In most cases, you will want to leave at least one instance in each of
your auto scaling groups unprotected. If all of the instances are
protected, no scale in action will be taken.
Link
I have foreseen a problem that could happen with my application but I am unsure if it is possible to solve, and perhaps the architecture needs to be redesigned.
I am using an AutoScalingGroup (ASG) on AWS to create EC2 instances that host game servers that players can join. At the moment, the ASG is scaled manually via a matchmaking API which changes the desired capacity based on its needs. The problem occurs when a game server is finished.
When a game finishes, it signals to the matchmaker that it is finished and needs terminating, and the matchmaker will then scale down the ASG accordingly, however, it doesn't seem to know exactly which instance to remove, and it won't necessarily be the one that needs terminating.
I can terminate the instance, but then as the ASG desired capacity is never changed when the instance is terminated, another server is created.
Is there a way I can scale down the ASG, as well as specifying which servers to remove from the group?
In a nutshell, the default termination policy during scale in is designed to remove instances that use the oldest launch configuration.
Currently, Amazon EC2 Auto Scaling supports the following termination policie:
OldestInstance Terminate the oldest instance in the group. This option is useful when you're upgrading the instances in the Auto Scaling group to a new EC2 instance type. You can gradually replace instances of the old type with instances of the new type.
NewestInstance Terminate the newest instance in the group. This policy is useful when you're testing a new launch configuration but don't want to keep it in production.
OldestLaunchConfiguration Terminate instances that have the oldest launch configuration. This policy is useful when you're updating a group and phasing out the instances from a previous configuration.
ClosestToNextInstanceHour Terminate instances that are closest to the next billing hour. This policy helps you maximize the use of your instances and manage your Amazon EC2 usage costs.
Default Terminate instances according to the default termination policy. This policy is useful when you have more than one scaling policy for the group.
Instance protection
One of the possible solutions could be to use Instance protection. The auto-scaling provides an instance protection to control whether instance can be terminated when scaling-in.
Therefore, enable the instance protection for ASG to protect instances from scaling-in by default. Once you are done with you server, decrease a value of desired number of instances, remove instance protection from particular instance (either using CLI or SDK; note that this protection remains enabled for the rest of instances) and auto-scaling will terminate that exact instance.
For more information about instance protection, see Instance Protection
The oldest server is removed. If you want to scale down a specific server, you will have to kill that server before changing desired capacity.
We have a terraform deployment that creates an auto-scaling group for EC2 instances that we use as docker hosts in an ECS cluster. On the cluster there are tasks running. Replacing the tasks (e.g. with a newer version) works fine (by creating a new task definition revision and updating the service -- AWS will perform a rolling update). However, how can I easily replace the EC2 host instances with newer ones without any downtime?
I'd like to do this to e.g. have a change to the ASG launch configuration take effect, for example switching to a different EC2 instance type.
I've tried a few things, here's what I think gets closest to what I want:
Drain one instance. The tasks will be distributed to the remaining instances.
Once no tasks are running in that instance anymore, terminate it.
Wait for the ASG to spin up a new instance.
Repeat steps 1 to 3 until all instances are new.
This works almost. The problem is that:
It's manual and therefore error prone.
After this process one of the instances (the last one that was spun up) is running 0 (zero) tasks.
Is there a better, automated way of doing this? Also, is there a way to re-distribute the tasks in an ECS cluster (without creating a new task revision)?
Prior to making changes make sure you have the ASG spanned across multiple availability zones and so are the containers. This ensures High Availability when instances are down in one Zone.
You can configure an update policy of Autoscaling group with AutoScalingRollingUpgrade where you can set MinInstanceInService and MinSuccessfulInstancesPercent to a higher value to maintain slow and safe rolling upgrade.
You may go through this documentation to find further tweaks. To automate this process, you can use terraform to update the ASG launch configuration, this will update the ASG with a new version of launch configuration and trigger a rolling upgrade.
I am looking at using AWS auto-scaling to scale my infrastructure up and down based on various performance metrics (CPU, etc.). I understand how to set this up; however, I don't like that instances are terminated rather than stopped when it is scaled down. This means that when I scale back up, I have to start from scratch with a new instance and re-install my software, etc. I'd rather just start/stop my instances as needed rather than create/terminate. Is there a way to do this?
No, it is not possible to Stop an instance under Auto Scaling. When a Scaling Policy triggers the removal of an instance, Auto Scaling will always Terminate the instance.
However, here's some ideas to cope with the concept of Termination...
Option 1: Use pre-configured AMIs
You can configure an Amazon EC2 instance with your desired software, data and settings. Then, select the EC2 instance in the Management Console and choose the Create Image action. This will create a new Amazon Machine Image (AMI). You can then configure Auto Scaling to use this AMI when launching a new instance. Each new instance will contain exactly the same disk contents.
It's worth mentioning that EBS starts up very quickly from an AMI. Instead of copying the whole AMI to the boot disk, it copies it across on "first access". This means the new instance can start-up immediately rather than waiting for the whole disk to be copied.
Option 2: Use a startup (User Data) script
Each Amazon EC2 instance has a User Data field, which is accessible from the instance. A script can be passed through the User Data field, which is then executed when the instance starts. The script could be used to install software, download data and configure the instance.
The script could do something very simple, like download a configuration script from a source code repository, then execute the script. This means that machine configuration can be centrally managed and version-controlled. Want to update your app? Just launch a new instance with the updated script and throw away the old instance (which is much easier than "updating" an app).
Option 3: Add/Remove instances to an Auto Scaling group
Rather than using Scaling Policies to Launch/Terminate instances for an Auto Scaling group, it is possible to attach/detach specific instances. Thus, you could 'simulate' auto scaling:
When you want to scale-down, detach an instance from the Auto Scaling group, then stop it.
When you want to add an instance, start the instance then attach it to the Auto Scaling group.
This would require your own code, but it is very simple (basically two API calls). You would be responsible for keeping track of which instance to attach/detach.
You can suspend scaling processes, see documentation here:
https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-suspend-resume-processes.html#as-suspend-resume
Add that instance to Scale in protection and then stop the instance then it will not delete your instance as it's having the scale in protection.
Actually you have three official AWS options to reboot or even stop an instance which belongs to an Auto Scaling Group:
Put the instance into the Standby state
Detach the instance from the group
Suspend the health check process
Ref.: https://aws.amazon.com/premiumsupport/knowledge-center/reboot-autoscaling-group-instance/
As of April 2021:
Option 4: Use Warm Pools and an Instance Reuse Policy
By default, Amazon EC2 Auto Scaling terminates your instances when your Auto Scaling group scales in. Then, it launches new instances into the warm pool to replace the instances that were terminated.
If you want to return instances to the warm pool instead, you can specify an instance reuse policy. This lets you reuse instances that are already configured to serve application traffic.
This mostly automates option 3 from John's answer.
Release announcement: https://aws.amazon.com/blogs/compute/scaling-your-applications-faster-with-ec2-auto-scaling-warm-pools/
Documentation: https://docs.aws.amazon.com/autoscaling/ec2/userguide/ec2-auto-scaling-warm-pools.html
This is to expand a little on #mwalling's answer, because that is the right direction, but needs a little extra work to prevent instance termination.
There is now a way to stop or hibernate scaled in instances!
By default AWS Autoscaling scale in policy is to terminate an instance. Even if you have a warm pool configured. Autoscaling will create a fresh instance to put into the warm pool. Presumably to make sure you start with a fresh machine every time. However, with a instance reuse policy you can make AWS Autoscaling either stop or hibernate a running instance and store that instance in the warm pool.
Advantages include:
Local caches stay populated (use hibernate for in memory cache).
Burstable EC2 instances (those types with T*) keep built up burst credits instead of the newly created instance that have limited or no credits.
Practical example:
We use a burstable EC2 instance for CI/CD work that we scale to 0 instances outside working hours. With a reuse policy our local image repository stays populated with the most important Docker images. Also we keep the built up credit from the previous day and that speeds up automatic jobs we run first thing every morning.
How to implement:
There's currently no way of doing this completely via the management console. So you will need to use AWS CLI or SDK.
First create a warm pool as described in the AWS Documentation
Then execute this command to add a reuse policy:
aws autoscaling put-warm-pool --auto-scaling-group-name <Name-of-autoscaling-group> --instance-reuse-policy ReuseOnScaleIn=true
Reference docs for the command: AWS CLI Autoscaling put-warm-pool documentation
Flow diagram of possible life cycles of EC2 instances:
Image from AWS Documentation: Lifecycle state transitions for instances in a warm pool