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The full description of creating lambda
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@sagidM
sagidM authored Sep 10, 2017
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Static website hosting
```xml
<RoutingRules>
<RoutingRule>
<Condition>
<KeyPrefixEquals/>
<HttpErrorCodeReturnedEquals>404</HttpErrorCodeReturnedEquals>
</Condition>
<Redirect>
<Protocol>https</Protocol>
<HostName>__DOMAIN__</HostName>
<ReplaceKeyPrefixWith>__PATH_TO_LAMBDA__?path=</ReplaceKeyPrefixWith>
<HttpRedirectCode>307</HttpRedirectCode>
</Redirect>
</RoutingRule>
</RoutingRules>
```
## What is it?

It's AWS Lambda, which is a compute service that lets you run code without provisioning or managing servers.
> _[Read more about AWS Lambda.](http://docs.aws.amazon.com/lambda/latest/dg/welcome.html)_
Bucket policy
```json
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AddPerm",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::__BUCKET_NAME__/*"
}
]
}
```

## What this lambda provides
Let's say we have some _shared image_ in **S3**, for example:
`https://example.com/images/pretty_photo.jpg`

to resize this image to _150x150_, for instance, on fly we can make a request like this:
`https://example.com/images/150x150/pretty_photo.jpg`

So, if there's not image in this path, it's redirected to lambda and, after a moment, lambda creates the suitable image and then redirects back. We'll obviously have a new image next time.

Role policy document
***
Instead of `WxH` there're some extra available _magic paths_:
`.../AUTOx150/...`
`.../150xAUTO/...`
or
`.../150x150_max/...`
`.../150x150_min/...`

> Note that **s3-resizer** **don't enlarge an image** if the original image width or height are already less than required dimensions. You can read about **[#withoutEnlargement](http://sharp.dimens.io/en/stable/api-resize/#withoutenlargement)** method.

## Setting up

#### To resize images we need a storage, which is _S3_, and _Lambda_ function. Then we should set up redirection rules.

* Create a **Bucket**
* * Go to [Services -> Storage -> S3](https://s3.console.aws.amazon.com/s3/home)
* * Click on the blue button **Create bucket**
* * Enter the name and click on **Create**

* Create a **Lambda**
* * Go to [Services -> Compute -> Lambda](https://console.aws.amazon.com/lambda/home)
* * Click on the orange button **Create a function**
* * In the next page, click on the similar button **Author from scratch**
* * Add a trigger, which would listen to http requests (you also would be able to do it later)
* * * On the dotted square choose **API Gateway**
* * * You can use default **API name** or create new one
* * * In **Security** select **Open**, then click **Next**
* * In **Configure function** page
* * * Name a new lambda
* * * In **Runtime** select **Node.js 6.10**
* * * Upload a _.zip_ file (download it from [releases](https://github.com/kofon95/s3-resizer/releases))
* * * > You'll also need to set up two **Environment variables**, with _BUCKET_ and _URL_ as keys. But in this time, you don't know about that _URL_. It is **endpoint** which you'll see below.
* * * Choose role which has permission to put any object or create a new one. To do that
* * * * choose **Create a custom role** in role's list. It should open a new page in your browser. On that page
* * * * choose **Create a new IAM Role**
* * * * name you role, for example: *"access_to_putObject"*
* * * * Expand **View Policy Document**, click **Edit**, and write this content:
```json
{
"Version": "2012-10-17",
Expand All @@ -56,3 +72,98 @@ Role policy document
]
}
```
> Pay attention to `__BUCKET_NAME__`
* * * That page should closes after that action. So go on creating a lambda. And take a look at **Advanced settings**
* * * * Allocate a memory 512
* * * * Timeout could be 5 seconds
> It's mooore than enough. And you shouldn't care of limits because images caches, which means lambda calls only for the first time.
* * * Click **Next**, **Create function**. And wait for 20-30 seconds. Lambda is created.

***

* Public access to files in your bucket and relationships between lambda and bucket.
* * Firstly, you need Lambda's _url_
* * * Click the link of **API name** (in case you didn't change it in creating lambda, it should name like **LambdaMicroservice**)
* * * On the new page, look for **Actions** button, select **Deploy API** and choose **prod** in **Deployment stage**. Then click **Deploy**
* * * Expand **prod** in **Stages**, click on **GET** and copy URL that you see
* * Open your created bucket -> Permissions -> Bucket Policy
* * Paste this pease of code there and click **Save**
```json
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AddPerm",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::__BUCKET_NAME__/*"
}
]
}
```
> Pay attention to `__BUCKET_NAME__`. By the way, you're able to open access not to whole bucket but to specific directory specifying it instead of __*__.
* * Go to Properties (near to Permissions) -> Static website hosting -> Select **"Use this bucket to host a website"**
* * In **Index document** paste any file, it'd be logical to name it _"index.html"_
* * Paste this **Redirection rules**
```xml
<RoutingRules>
<RoutingRule>
<Condition>
<KeyPrefixEquals/>
<HttpErrorCodeReturnedEquals>404</HttpErrorCodeReturnedEquals>
</Condition>
<Redirect>
<Protocol>https</Protocol>
<HostName>__DOMAIN__</HostName>
<ReplaceKeyPrefixWith>__PATH_TO_LAMBDA__?path=</ReplaceKeyPrefixWith>
<HttpRedirectCode>307</HttpRedirectCode>
</Redirect>
</RoutingRule>
</RoutingRules>
```
> Pay attention to `__DOMAIN__` and `__PATH_TO_LAMBDA__` (protocol is always _https_)
> For example, lambda's url is `https://some-id.execute-api.us-east-1.amazonaws.com/prod/your-lambdas-name`, the correct xml nodes must looks like
```xml
<HostName>some-id.execute-api.us-east-1.amazonaws.com</HostName>
<ReplaceKeyPrefixWith>prod/your-lambdas-name?path=</ReplaceKeyPrefixWith>
```
* * At this state, copy your **Endpoint** and click save
* * Go to your lambda -> **Code** and set up these two **Environment variables** _(format: key=value)_
**BUCKET**=_your bucket's name_
**URL**=**Endpoint** you copied before
* * **Save** it. You've done!

***

* Test your lambda (optional)
* * Upload an image to your bucket and copy link to it. Check if the image shows in your browser
> Attention. That link must be of your **Endpoint** (website hosting). It make by concatinating **"$endpoint_url/$path_to_image/$image_name"**
* * Go to lambda, click on **Test**, and paste this json:
```json
{
"queryStringParameters": {"path": __YOUR_IMAGE_PATH_WITH_SIZE_PREFIX__}
}
```
> `__YOUR_IMAGE_PATH_WITH_SIZE_PREFIX__` - for example: `150x150/pretty_image.jpg`
* * Go back to the bucket, a new directory _150x150_ must be created


## Some patterns
This is some pattern which you can use in the models:
```ruby
IMAGE_PATH = "#{YOUR_ENDPOINT_URL}/uploads/images/models/"

def images()
img = self.image_name

return {
original: "#{IMAGE_PATH}#{img}",
big: "#{IMAGE_PATH}1000x1000_max/#{img}",
small: "#{IMAGE_PATH}450x450_max/#{img}",
thumb: "#{IMAGE_PATH}128x128_max/#{img}"
}
end
```

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