AWS Shop example: API Gateway (2)

Introduction

Last time, I talked about the API Gateway [1]. The URL that we used last time has randomness in it: it looks like https://54dwcigu3a.execute-api.eu-west-1.amazonaws.com/prod/shop. When you destroy the API Gateway objects and redeploy them, you will get another URL. That’s not nice: we don’t want to change the URL in all our cashing machines when we deploy a new version of our software… The objects we used in the last blog are shown in the next image:

Today, I will use the domain retsema.eu (which is running in Route53, the DNS of AWS) to show you what you need to configure to get the nicely formed url (like https://amis.retsema.eu/shop). When I really would own a shop, I would most probably call it something like https://api.retsema.eu/shop. But well, in this example I added AMIS as a prefix for everything, so I will use it for my URL as well.

Here’s the image that shows the objects that we will look at today:

Certificate

First, we need to have a certificate for our domain. Go to the certificate manager service, and click on the arrow next to the checkbox of the certificate.

You can now see the details of the certificate:

The name of the certificate is *.retsema.eu, which means that I can use this certificate for any name that ends with retsema.eu. The certificate is issued by Amazon (I also could have uploaded a certificate that is issued by someone else).

When you request a certificate from Amazon, there are two ways that Amazon can verify that you really are the owner of the domain. The first way, is to verify by e-mail. The disadvantage is that this is slow: you are dependent on people to read the e-mail, press a link etc.

A much faster way, is to check via DNS. Amazon asks you to add an alias (CNAME) record to your domain, which will point to an AWS address. You can see how this works, by clicking on the “Export DNS configuration to a file” link.

When you open the file, you can see that there has to be a record in the DNS with the name “_737c89388ce141925aefa00b332f8de1.retsema.eu.” and that record has to point at “_37812d6ffa713cfcf8ebc1117fc2f271.nhqijqilxf.acm-validations.aws.” When AWS verifies the domain (sometimes this is done within minutes, sometimes it takes more then two days), they will use the url _737c89388ce141925aefa00b332f8de1.retsema.eu. to check if they are routed to _37812d6ffa713cfcf8ebc1117fc2f271.nhqijqilxf.acm-validations.aws.

Before we go and look at Route53, I’d like to point to a nice detail in this screen. You see, that when the certificate is in use, this screen will show you where it is used (“Associated resources”). Though I never implemented a load balancer anywhere (see the architecture image), my certificate is used in three load balancers. It seems that the API Gateway uses multiple load balancers to do its job…

Route 53

Let’s look at the CNAME record: go to the Route53 service. In the dashboard, you can see that I have three public domain names, and six hosted zones. That means that I use three private zones and three public zones.

Click on the “Hosted zones” link, you will see the retsema.eu domain name in this list (normally you would see all six domain names here, I removed the other domain names from the image because they are not used in the shop example and some of them can be confusing). Click on the link with your domain name (in this case: retsema.eu):

In this screen, you see all the DNS records for the retsema.eu domain. When you click on the CNAME record that we talked about, then the details are shown on the right part of the screen:

You can already see the amis.retsema.eu entry. But before we look into that, we have to change the configuration of the API Gateway.

API Gateway

Go to the API Gateway, and choose Custom domain names in the left menu:

Click on the domain name amis.retsema.eu:

This might be confusing: we need to specify the full domain name (including the amis part) here, where only retsema.eu is a domain name. When you scroll down, you see API mappings:

You can see that amis.retsema.eu will use the prod stage, and that it will not have a path. This means that when 1we use amis.retsema.eu/shop, we always will use the prod stage and that we will have to specify the /shop resource when we use this URL.

It is possible to have multiple “nice URL’s” to the same API Gateway. Let’s try this out: let’s make a new URL api.retsema.eu that points to the same API Gateway. Click on Create:

Enter the name of the end point (in our case: api.retsema.eu) and add the certificate:

You also see the option to create a regional endpoint or an edge-optimized endpoint. A regional endpoint assumes that the people who use this URL will be in the neighborhood of the AWS region that this solution is deployed in (in my case: Frankfurt, AWS region eu-central-1).

When you would use an API Gateway to provide information (REST GET requests) and your company is a global company, then you could use the edge locations of AWS. These edge locations are in the neighborhood of your clients, and will cache the results of the API calls. This will speed up the process. In our case, Regional is good.

Now, scroll to the bottom of the screen and press save.

We have to do one more thing: scroll down, and look at the API mappings: they are empty now. Press on Configure API mappings:

In this screen, click on Add new mapping:

Click on the drop down windows for API and Stage, and choose the AMIS_api_gateway for API and prod for Stage. Leave the path empty. After that, press Save.

Route53

Now we have configured api.retsema.eu in the API gateway, we can configure the DNS entry: go back to the Route53 screen, and click on Create record set:

You might get confused here. We will need to create an A record. An A record in the DNS points to an IP address. But in the main screen, you see that amis.retsema.eu has an A record that points to an AWS address. That magic is done by clicking on the “Yes” radio button from the Alias:

You now can choose the Alias Target. When you scroll down, you see the API Gateway API. Choose it:

You can select Evaluate yes for Target Health: in that way, AWS will check regularly if the target (the load balancers of the API Gateway) are present and only point to healthy load balancers. After that, click Create:

But wait… We are talking about an A record. A records point to IP adresses, they are not supposed to point to other services. Is api.retsema.eu really an A record? Let’s wait a few minutes and then find out by checking the DNS:

You see that it is indeed a normal A record, giving back only IP addresses. Route53 has put the IP addresses from the load balancers of the API Gateway in this DNS record. We could also check this from within AWS: click on the api.retsema.eu record, and then on Test record set:

In the next screen, you can simulate to check from another location than you are now, by specifying an IP address to test from. In our case, this isn’t necessary, so we will leave the Resolver IP address as it is and press the Get response button, you will see the response on the right part of the screen:

And, because the proof of the pudding is in the eating, let’s use our new api.retsema.eu record to send a message to the API gateway:

[vagrant@localhost client]$ ./encrypt_and_send.py AMIS1 https://api.retsema.eu/shop

Shop id = AMIS1

Key alias = alias/KeyL-AMIS1

URL = https://api.retsema.eu/shop

Data = {“shop_id”: “AMIS1”, “content_base64”: “KW4JaTQy3R4kOvJsK669coHgPspVuTUwBve5v9D4m2OpsXWTx+u3adAR70Oi8CCEMA+Tits7PzjuBNQBwNZg0Iyn0yMW4LeEFrcaJh84+m8DOECmVuYLdmyHmpKzVOl4XkiQ4w4wEnf3NgrE67hmolpOL4zxfTS7DFzpXeusc6rDfXLPHSSQ8kHkXx9/S6y6yovQM4yWQHXx6CdvJ9+dzynTLew5B/ClAPKon3XPeB5S7uNHWyoTPDH0GP9CI6rungnLyY52l3H17d7StsWa5en1EYHTHBQ5Jpsb4ini5TqAiFtfah8oZuU4VuWBtC3k4aLIli0LwEPgIyOIuZfRHQ==”}

request_number = 1

Status code = 200

Content = b'”OK”‘

[vagrant@localhost client]$

Play along

I scripted the solution [2]. You can follow along and create this solution in your own environment, see the README.md file in the vagrant directory and see the introduction blog for more information. For this specific blog, you need your own domain. Replace retsema.eu by your own domain name. A domain name for .nl in AWS costs about $10 per year.

Links

[1] This is the fifth blog about this shop. Links to the previous blogs:

– Introduction: https://technology.amis.nl/2020/04/26/example-application-in-aws-using-lambda/

– Lambda and IAM: https://technology.amis.nl/2020/04/29/aws-shop-example-lambda/

– SNS: https://technology.amis.nl/2020/05/02/aws-shop-about-the-aws-simple-notification-service-sns/

– DynamoDB: https://technology.amis.nl/2020/05/05/aws-shop-dynamodb-the-aws-nosql-database/

– API Gateway (1): https://technology.amis.nl/2020/05/09/aws-shop-api-gateway-1/

[2] https://github.com/FrederiqueRetsema/AMIS-Blog-AWS , directory shop-1

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