Added AWS S3 tutorial.

doc/AWS_S3_Tutorial.md

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+# Setting up Restic with Amazon S3
+
+## Preface
+
+This tutorial will show you how to use Restic with AWS S3. It will show you how
+to navigate the AWS web interface, create an S3 bucket, create a user with
+access to only this bucket, and finally how to connect Restic to this bucket.
+
+## Prerequisites
+
+You should already have a `restic` binary available on your system that you can
+run. Furthermore, you should also have an account with
+[AWS](https://aws.amazon.com/). You will likely need to provide credit card
+details for billing purposes, even if you use their
+[free-tier](https://aws.amazon.com/free/). 
+
+
+## Logging into AWS
+
+Point your browser to
+https://console.aws.amazon.com
+and log in using your AWS account. You will be presented with the AWS homepage:
+![AWS Homepage](img/s3/01_aws_start.png?raw=true)
+
+By using the "Services" button in the upper left corder, a menu of all services
+provided by AWS can be opened:
+![AWS Services Menu](img/s3/02_aws_menu.png?raw=true)
+
+For this tutorial, the Simple Storage Service (S3), as well as Identity and
+Access Management (IAM) are relevant.
+
+
+## Creating the bucket
+
+First, a bucket to store your backups in must be created. Using the "Services"
+menu, navigate to S3. In case you already have some S3 buckets, you will see a
+list of them here:
+![List of S3 Buckets](img/s3/03_buckets_list_before.png?raw=true)
+
+Click the "Create bucket" button and choose a name and region for your new
+bucket. For the purpose of this tutorial, the bucket will be named
+`restic-demo` and reside in Frankfurk. Because the bucket namespace is shared among all AWS users, the
+name `restic-demo` may not be available to you. Be creative and choose a unique
+bucket name.
+![Creating a Bucket](img/s3/04_bucket_create_start.png?raw=true)
+
+It is not necessary to configure any special properties or permissions of the
+bucket just yet. Therefore, just finish the wizard without making any further
+changes:
+![Reviewing Bucket Creation](img/s3/05_bucket_create_review.png?raw=true)
+
+The newly created `restic-demo` bucket will no appear on the list of S3
+buckets:
+![List With New Bucket](img/s3/06_buckets_list_after.png?raw=true)
+
+
+## Creating a user
+
+Use the "Services" menu of the AWS web interface to navigate to IAM. This will
+bring you to the IAM homepage. To create a new user, click on the "Users" menu
+entry on the left:
+![IAM Homepage](img/s3/07_iam_start.png?raw=true)
+
+In case you already have set-up users with IAM before, you will see a list of
+them here. Use the "Add user" button at the top to create a new user:
+![IAM User List](img/s3/08_user_list.png?raw=true)
+
+For this tutorial, the new user will be named `restic-demo-user`. Feel free to
+choose your own name that best fits your needs. This user will only ever access
+AWS through the `restic` program and not through the web interface. Therefore,
+"Programmatic access" is selected for "Access type":
+![Choosing Username And Access Type](img/s3/09_user_name.png?raw=true)
+
+During the next step, permissions can be assigned to the new user. To use this
+user with Restic, it only needs access to the `restic-demo` bucket. Select
+"Attach exiting policies directly", which will bring up a list of pre-defined
+policies below. Afterwards, click the "Create policy" button to create a custom
+policy:
+![Assigning a Policy](img/s3/10_user_pre_policy.png?raw=true)
+
+A new browser window or tab will open with the policy wizard. In Amazon IAM,
+policies are defined as JSON documents. For this tutorial, the "Policy
+Generator" will be used to generate a policy file using a web interface:
+![Creating a New Policy](img/s3/11_policy_start.png?raw=true)
+
+After invoking the policy generator, you will be presented with a user
+interface to generate individual permission statements. For Restic to work, two
+such statements must be created. The first statement is set up as follows:
+
+```
+Effect: Allow
+Service: S3
+Actions: DeleteObject, GetObject, PutObject
+Resource: arn:aws:s3:::restic-demo/*
+```
+
+This statement allows Restic to create, read and delete objects inside the S3
+bucket named `restic-demo`. Adjust the bucket's name to the name of the bucket
+you created earlier. Using the "Add Statement" button, this statement can be
+saved. Now a second statement is created:
+
+```
+Effect: Allow
+Service: S3
+Actions: ListBucket
+Resource: arn:aws:s3:::restic-demo
+```
+
+Again, substitute `restic-demo` with the actual name of your bucket. Note that,
+unlike before, there is no `/*` after the bucket name. This statement allows
+Restic to list the objects stored in the `restic-demo` bucket. Again, use "Add
+Statement" to save this statement. The policy creator interface should now
+look as follows:
+![Policy Creator With Two Statements](img/s3/12_policy_permissions_done.png?raw=true)
+
+Continue to the next step and enter a name and description for this policy. For
+this tutorial, the policy will be named `restic-demo-policy`. In this step you
+can also examine the JSON document created by the policy generator. Click
+"Create Policy" to finish the process:
+![Policy Review](img/s3/13_policy_review.png?raw=true)
+
+Go back to the browser window or tab where you were previously creating the new
+user. Click the button labeled "Refresh" above the list of policies to make
+sure the newly created policy is available to you. Afterwards, use the search
+function to search for the `restic-demo-policy`. Select this policy using the
+checkbox on the left. Then, continue to the next step.
+![Attaching Policy To User](img/s3/14_user_attach_policy.png?raw=true)
+
+The next page will present an overview of the user account that is about to be
+created. If everything looks good, click "Create user" to complete the process:
+![User Creation Review](img/s3/15_user_review.png?raw=true)
+
+After the user has been created, its access credentials will be displayed. They
+consist of the "Access key ID" (think username), and the "Secret access key"
+(think password). Copy these down to a safe place.
+![User Credentials](img/s3/16_user_created.png?raw=true)
+
+You have now completed the configuration in AWS. Feel free to close your web
+browser now.
+
+
+## Initializing the Restic repository
+
+Open a terminal and make sure you have the `restic` binary ready. First, choose
+a password to encrypt your backups with. In this tutorial, `apg` is used for
+this purpose:
+
+```console
+$ apg -a 1 -m 32 -n 1 -M NCL
+I9n7G7G0ZpDWA3GOcJbIuwQCGvGUBkU5
+```
+
+Note this password somewhere safe along with your AWS credentials. Next, the
+configuration of Restic will be placed into environment variables. This will
+include sensitive information, such as your AWS secret and repository password.
+Therefore, make sure the next commands **do not** end up in your shell's
+history file. Adjust the contents of the environment variables to fit your
+bucket's name and your user's API credentials.
+
+```console
+$ unset HISTFILE
+$ export RESTIC_REPOSITORY="s3:https://s3.amazonaws.com/restic-demo"
+$ export AWS_ACCESS_KEY_ID="AKIAJAJSLTZCAZ4SRI5Q"
+$ export AWS_SECRET_ACCESS_KEY="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"
+$ export RESTIC_PASSWORD="I9n7G7G0ZpDWA3GOcJbIuwQCGvGUBkU5"
+```
+
+After the environment is set up, Restic may be called to initialize the
+repository:
+
+
+```console
+$ ./restic init
+created restic backend b5c661a86a at s3:https://s3.amazonaws.com/restic-demo
+
+Please note that knowledge of your password is required to access
+the repository. Losing your password means that your data is
+irrecoverably lost.
+```
+
+Restic is now ready to be used with AWS S3. Try to create a backup:
+
+```console
+$ dd if=/dev/urandom bs=1M count=10 of=test.bin
+10+0 records in
+10+0 records out
+10485760 bytes (10 MB, 10 MiB) copied, 0,0891322 s, 118 MB/s
+
+$ ./restic backup test.bin
+scan [/home/philip/restic-demo/test.bin]
+scanned 0 directories, 1 files in 0:00
+[0:04] 100.00%  2.500 MiB/s  10.000 MiB / 10.000 MiB  1 / 1 items ... ETA 0:00 
+duration: 0:04, 2.47MiB/s
+snapshot 10fdbace saved
+
+$ ./restic snapshots
+ID        Date                 Host        Tags        Directory
+----------------------------------------------------------------------
+10fdbace  2017-03-26 16:41:50  blackbox                /home/philip/restic-demo/test.bin
+```
+
+A snapshot was created and stored in the S3 bucket. This snapshot may now be
+restored:
+
+```console
+$ mkdir restore
+
+$ ./restic restore 10fdbace --target restore
+restoring <Snapshot 10fdbace of [/home/philip/restic-demo/test.bin] at 2017-03-26 16:41:50.201418102 +0200 CEST by philip@blackbox> to restore
+
+$ ls restore/
+test.bin
+```
+
+The snapshot was successfully restored. This concludes the tutorial.
+