Add HOWTO get ECS-related log

docs/HOWTO-get-ecs-logs.md

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+## Step 1: Find the public IP address of BastionHost
+1. Log in AWS Console
+2. Go to AWS CloudFormation under `Service` > `Management Tools`
+3. On column `Stack Name`, click on the link named `<your stack name>-BastionHost-<a string>`. For example, `hacko18-BastionHost-10CS5LU2DG10L`
+4. Under the `Resoures` section, click on the link on `Physical ID` column. You will be directed to the `Instances` section of the `Service`/`EC2` page. There will be 1 row in the table.
+5. In the description of the pre-selected ec2 instance, look for the value of `IPv4 Public IP` field. This is the public IP address of the BastionHost.
+
+## Step 2: Find the private IP address of the EC2 instance that hosts the ECS containers
+1. Log in AWS Console
+2. Go to `Services` > `Elastic Container Service`
+3. Under the `ECS Instances` tab, on column `Service Name`, find the container instance that you want to get logs from by clicking on each of them one by one under the `Container Instance` column and look at what `Task Definition` they are running
+4. Once you found the container instance you're looking for, go back to the table in \#3 above and click its corresponding link under the `EC2 Instance` column
+5. Get the private IP address of this EC2 instance the same way as described in \#5 of Step 1 above.
+
+## Step 3: Get all the logs from ECS to your local machine 
+1. Copy your aws account private key to the BastionHost by `scp -i <path to your aws account's private key> <**absolute path** to your aws account's private key> ec2-user@<BastionHost ip>
+2. ssh into the BastionHost by `ssh -i <path to your aws account's private key file> ec2-user@<BastionHost's IP> ec2-user@<BastionHost ip>
+3. Once you are in BastionHost, use `ls` to confirm you have the private key at the current directory. Then, ssh into the EC2 instance by `ssh -i <path to the private key> ec2-user@<EC2 instance's private IP>
+4. Once you are in that EC2 instance, get the AWS ECS Log Collector by `curl -O https://raw.githubusercontent.com/awslabs/ecs-logs-collector/master/ecs-logs-collector.sh`
+5. Run the script with `sudo bash ./ecs-logs-collector.sh`
+6. There will be a archived file of all the logs named `collect.tgz` at the same director as you ran the script. Verify that this file exists and has a good amount of info by `ls -lh collect.tgz`
+7. Exit the EC2 Instance (you are now back in the BastionHost)
+8. Transfer the archived log file from the EC2 instance to BastionHost (where you are now) with `scp -i <path to your private key on BastionHost> ec2-user@<private IP of EC2 instance>:/home/ec2-user/collect.tgz .` (don't miss the dot at the end of this command)
+9. Exit the BastionHost (you are now back in your local machine)
+10. Transfer the archived log file from BastionHost to your local machine by `scp -i <path to your private key> ec2-user@<IP of BastionHost>:/home/ec2-user/collect.tgz .`
+11. Verify the archived log file is finally in your local machine by `ls -lh ./collect.tgz`
+12. Extract the archived log file with `tar xzfv collect.tgz`
+13. All the ECS logs is under `./collect/system/` directory
+
+## Related Information
+- [About ECS log](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/logs.html)
+- [About ECS log collector](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-logs-collector.html)
+
+TODO:
+- [ ] Write a script that get the IPs
+- [ ] Write a wrapper script around this AWS logs collector