This is more an informational post that may help others to feel less miserable in the same situation as I was! The scenario is this:
You are updating an ECS cluster via AWS CloudFormation but for whatever reason the cluster doesn’t stabilize. So, you see the stack is in
UPDATE_IN_PROGRESS state and you don’t receive any message in CloudFormation
Events page. If you can’t troubleshoot the issue with ECS and take no action, It will take 3 hours before CloudFormation timeouts and display a message! At this point, as you can guess, CloudFormation will rollback. Situation can be even worse if Rollback can not be proceeded successfully (in our case, there was a lack of resources preventing update and rollback). Again, CloudFormation will stuck in
UPDATE_ROLLBACK_IN_PROGRESS state and will timeout after 3 hours! In a conversation I had with AWS support, they said this time is hard-coded and can’t be changed at the moment!
So, in such a situation: Keep Calm And Troubleshoot!
Lambda functions are just another great tool provided by AWS to solve issues in a modern way! Using Lambda functions, you can run a micro service without a need to have a server and think of how to configure and maintain it!
There are lots of use cases for Lambda functions; here I used it to implement a service which sends alerts in case there is a slow query running in RDS. Of course slow queries are important for developers as it helps them to debug better and improve performance of the application. You can find the code here but there are some other things to be considered:
- As you may know, there are some ways to trigger a Lambda function. In this case, using CloudWatch Events to schedule it periodically makes sense.
- The lamda function should have some permissions to get RDS Logs and send alerts using SNS. To find out how to define required rules, please see this AWS documentation. You are also asked to do this when creating Lambda function.
- There is a parameter named ‘distinguisher’ which is actually the keyword specifying the occurrence of slow query. For ‘Postgresql’ RDS it can be ‘
- Parameters Group in RDS should be configured to log slow queries. To know how to do this please see AWS documentation or this guide:Enabling slow query log on Amazon RDS
If you use ElasticSearch for Log analysis, you probably need to have backup and retirement strategy. It’s very handy to store a backup on a S3 bucket and configure lifecycle on that S3 bucket. I know there is a plugin (curator) that can do this but I preferred to use another approach and use ElasticSearch REST API’s. Here is a step to step guide about how to achieve this:
1) install AWS plugin:
2) create repository in your Elasticsearch cluster:
curl -XPUT 'localhost:9200/_snapshot/backup_s3_repository?pretty' -d'
"base_path": "DIRECTORY_NAME WITHIN BUCKET"
- AWS plugin should be installed on all nodes and services should be restarted to recognize plugin; otherwise you will get this error:
“Unknown [repository] type [s3]”
3) create snapshot:
curl -k -XPUT ‘https://localhost:9200/_snapshot/backup_s3_repository/snapshot_name?pretty?wait_for_completion=true’
4) create a cron job for taking snapshots (for step 3). You can skip `wait_for_completion=true` in cron job
5) Configure Lifecycle for that S3 bucket.
As I mentioned in my previous post, I would like to introduce a project I have recently started which is a Chef cookbook about system healthcheck.
The idea is to generate a healthcheck page based on results of running Serverspec tests. Specifically, it would be helpful for load balancers and more specifically for AWS ELB healthcheck. According to Serverspec: it tests your servers’ actual state by executing command locally, via SSH, via WinRM, via Docker API and so on. So you don’t need to install any agent softwares on your servers and can use any configuration management tools. But the true aim of Serverspec is to help refactoring infrastructure code. Load Balancers check health of system using this healthcheck URL and stop sending traffic if it’s not healthy. The generated health check page can be handy for this URL then. If self-check fails, it will return an error status code, otherwise 200 status code. In this cookbook, 2 concepts are used:
- Infrastructure test as code using Serverspec: It’s best if we have a test-driven infrastructure as code but even if there is no code for infrastructure, this cookbook can still help!
- Loadbalancer healthcheck: if healthchek page is comprehensive enough, this check can help in having a high available system. In case of AWS, when ELB is accompanied by Auto Scaling Group, a new healthy instance will replace the bad one if ELB notices an issue.
So, if you are interested in test driven coding especially in infrastructure, please have a look. Looking forward to hear your feedbacks.
I’m really a big fan of open source concept as I’ve seen its benefits in improving quality of the world we are living in. Especially in a country where access to high quality materials is hard, it’s the only legal and fair way to learn more and be able to contribute. The other way to access valuable data/tools actually is cheating! and I really hate that. I’m proud that I have never cheated in my whole educational life whereas it was really common to cheat and win! Open source development is also taking and giving which satisfies your spirit!
One of the things I really love working with public cloud (in specific, AWS) is its openness and nice documentation which enables everyone to implement their ideas that is in line with Open Source concept. In addition, AWS emphasis on DevOps and its integration with open source tools such as Chef, Packer, … has helped in fortifying open source culture in public cloud context. You can find great tools and utilities which are developed for AWS. In my next post, I will introduce a project that I have started and any contribution is more than welcomed!
I recently had difficulties using Chocolatey chef cookbook to install packages on Windows 2012 R2 EC2 instances via Packer. For those who have issues, I would recommend to use an older version of chocolatey cookbook (12_5_fix). A solution is to modify Berksfile with the following:
cookbook 'chocolatey', git: "https://github.com/chocolatey/chocolatey-cookbook.git", branch: "12_5_fix"
On the new exciting journey that I started in public cloud, today I earned AWS Solutions Architect (Associate Level) certificate. It was a bit more challenging than what I expected but it was fun! For those who want to pass the exam, in my opinion despite what’s said about the focus of exam on VPC, RDS, high availability and scalability; the truth is that you should get familiar with almost all of the services and update yourself with new ones. For example, to my surprise I didn’t have any direct question about RDS but instead 5 or 6 questions about SQS and SWF and 1 question about Kinesis! I suppose questions are randomly selected and others may have different experiences but it’s a good idea to know basics of all the services. Of course, VPC, security, high availability and scalability are super important and you must be fluent in them but all I say is that they are not enough for passing the exam. Also, expect more scenario sort of questions which include different concepts rather than direct one sentence questions that you may find in internet.
So, if you are preparing for this exam, work harder and good luck!