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EC2 instance

** 
volume == hard disk
security groups == virtual firewalls
--------------------------
EC2 instances types:
'Dr mc gift pix'
D-desnsity
R-ram
m-main choice (general)
c-compute
g-graphics
i-iops
f-fpga (field-programmable gate array)
t--cheap (t2 micro)
p-graphics(pics)
x-extreme
--------------------------

termination protection-off by default.
EBS will be deleted when EC2 instance is terminated by default.
EBS root volume of default AMI cann't be encrypted. but third party tools can be used to encrypt, or by making an image copy of the instance.
additinal volumes can be encrypted
-------------------

EBS: the block storage assiciated with an EC2 instance

pricing models:
-on demand
-spot
-reserved
-dedicated host

instances are charged by the hour-rounded up. unless aws terminated the instance, then it is rounded down.

ebs consists:
 ssd, general purpose - GP2 - (up to 10,000 iops)
 ssd, provisioned iops - IO1 - more then 10,000 iops
 hdd, thouroughput optimized ST1 - frequently accessed workloads
 hdd, cold SC1 - less frequenly accessed data
 hdd, magnectic - standard - cheap less frequenly accessed data

*can't connect more then 1 EC2 instance to 1 EBS. use EFS for that

----------------
instance termination protection is turned off by default.
the root(where OS is installed) EBS is deleted when the EC2 instance is terminated by default.
root volumes can't be encrypted unless using third party tools, but ither EBS volumes can be.
----------------
volumes exist on EBS - they are virtual hard disk.
snapshots (point in time copies of volumes) exits on S3.
taking a snapshot of a volume will store that volume on S3.
snapshots are incremental - only data that changed since the last snapshot are moved to S3
snapshots are encrypted automatically
volumes restored from snapshots are ecnrypted automatically
you can share snapshot, but only if they are un-encrypted.
you should stop the instance bofore taking a snapshot of a root volume
------------------
security rules:
all inbound traffic is blocked by defualt
all outbound traffic is allowed by default
can have any numbr or instances within a security group
can have multiple security groups attached to EC2 instances
there are no 'deny' rules. on allow
security groups are stateful - if you allow a rule for traffic in, that traffic is also allowed out. (access lists are not)
you can't block specific ip adresses from security groups.

---------------------
roles: are more secure then storing the access and secret keys on EC2. easier to manage.
can be assigned to instaces after they are provisions
roles can be updated during usage.
----------------------
raid = redundant aray of indipendent disks. acting as one disk to the OS.
raid 0 - good perfoamce. no data redundancy
raid 1 - mirrored, data redundancy
raid 5 - aws doesn't recommend this for EBS. good for reads, bad for writes
raid 10 - good redundancy and performance.

to increase IO - increase disk volumes as a raid
-----------------
taking a snapshot of a Raid array: (application consistent snapshot)
stop application from writing to disk by freezing the file system / unmount the raid array / shut down the EC2 instance
flush all caches to the disk
--------------------
when taking a snapshot of a volume, the snapshot is encrypted by default
volumes restored from encrypted snapshots are also encrypted
can't share encrypted snapshots.
------------------------
AMI - amazon machine image.
AMI's are available on the store.
AMis are regional - can only be launched from the region it is stored in. but you can copy AMIs to other region. using the cli api or console.
-------------------
AMI type: EBS backed and Instance Store backed (also called ephemeral).
Instance Stores can't attach additional Instnce Store Volumes after launching. 
EBS can be stopped and re-run on a different hypervisor in case of a problem. Instance Store can't.
Instance Stores are less durable, if their host fails - the instance is lost. (ephemeral)
EBS are created from a snapshot. Instance Store are created from a template stored on S3
both can be rebooted without losing data
-------------
elastic load balancer
classic / application
*a subnet == avalability zone
has healthchecks
no ip adress. only dns names.
----------------------
cloudwatch
standart monitoring - 5 mins, detaild monitoring - 1 min
create dashboard, alarms, events, logs
cloud watch is for logginng , monitoring. cloud trail is for auditing an entire aws env/ accounts.
-----------------------
credentials are normally stored on an instance under the .aws folder. this is a security breach..
roles allow instances not to have the credentials written to a file on the instance. therfore safer
roles are global. not by zone

---------------------------------
bash script example: 
#!/bin/bash
yum update -y
yum install httpd -y
service httpd start
chkconfig httpd on
aws s3 cp s3://mywebsitebucket-acg2/index.html /var/www/html

----------------
metadata:
curl http://169.254.169.254/latest/meta-data/

---------------------------
Autoscaling  groups require launch configuration before launching.
--------------
placement group - grouping of instances within a single availability zone. used for low network latency and high performace.
only certain types of instances can be part of  a placemnet group.
recommended to use homogenous instaces types (same size and family)
can't merge groups.
can't move existing instincaes into an existing group.
------------------------
efs - elastic file system.
pay for the storge you use.
allows to use a single storage across multiple ec2 instances. could use as a central file storage.
data is stored across multiple AZ
read after write consistency
*not available in all zones yet
----------------------
lambda - no servers, auto scaling, very cheap
-------------
summary

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