AWS Lamba Debugging - How to connect to an API on your local(host) machine

-

One of my recent bald-patch inducing struggles was to develop and test an AWS Lambda function that connects to a REST API to do some stuff. 

It is rather nice that you can deploy (using a local Docker container) and debug the said Lambda code in VSCode using the AWS Toolkit extension. In my case, the Lambda attempts to open a connection to a Django REST API which I had running in debug mode on my local machine (i.e. localhost interface).

Seems fairly straightforward. If you haven't previously, you'll probably soon run into the issue of opening an API connection to "localhost" from the Lambda code which doesn't work, since in the container context, that's the container's local connection, not the host's. 

So you need to point the API connection at host.docker.internal instead which is already mapped to your physical machine by Docker.

This works like a charm if you are doing straight forward things - like not using prefixes on your domain name. In my case, I was using the django-tenants package which differentiates multiple "customers" on a single database with different schemas, and it uses a name prefix, such as test.localhost to determine which database schema to connect to. The Docker localhost remapping is a one-to-one mapping - wildcards don't work - so trying to connect to test.host.docker.internal results in no connection reaching the host API.

There are a couple of configuration items to be aware of to make this whole scenario work:

On the Django API side:

  • In your Django settings.py file, you need to adjust your allowed hosts setting to include .host.docker.internal as this is name of the endpoint as far as the Lambda request is concerned.   

 

  • If you are launching your Django REST API from VSCode in order to debug it, make sure you edit your launch.json file to start the server with the "0.0.0.0:portnumber" argument to bind the server to all interfaces on your machine.

 


  • If you are specifically using django-tenants, make sure you add additional domain name entries for the tenant names you are testing into the domain table in your public schema database. For example, if your tenant primary schema name is "test.localhost", you will need to add "test.host.docker.internal" as a non-primary domain as well.

 

For the Lambda side:

  • For local debugging purposes, make sure you are trying to connect to your local Django API on port 8000 via "http://host.docker.internal:8000" instead of "http://localhost:8000".
  • Create and then edit your Lambda project's debug launch.json file and add the specific tenant prefix host mappings you need as a "--add-host" localArgument parameter under the "sam" configuration section. You can add multiple mappings - for example, to map "experiment" and "test" tenant domains to be passed to your localhost API:

 

  • In the above configuration, note that host-gateway is a docker-defined alias to your host machine.

Comments

Post a Comment

Popular posts from this blog

Solis S6 Pro (S6-EH1PxK-L-PRO) Hybrid Single Phase Inverter - Long Term Review

-
Image
Personally, I find the ability to be energy-self sufficient strangely exciting. With the ever decreasing cost of lithium batteries and solar panels, this has become tantalizingly more feasible, especially in countries with sunny climates, like that of South Africa where I currently live. Having had the opportunity to work with a few power inverters over the last few years, I thought I'd do a deeper dive into the particular inverter (and it's brethren) that has been powering my home for what is now approximately one and a half years. For context, my first inverter was a Goodwe 5048ES 4.6kW hybrid unit, which was silent and passively cooled. I never had any particular issues with it - but the software (including the inverter firmware) was best described as... mediocre. After four years with the Goodwe, I could see how having a bit more power capacity would be useful - requiring less planning in terms of what can be on when and at the same time.  I can't comment on newer Goodw...
Read more

Why Your Prepaid Electricity Meter Doesn't Work With Your Inverter And What To Do About It

-
In South Africa, prepaid electricity meters have become somewhat of a tenuous refuge from utility monopoly price gouging. In Johannesburg, you can expect to hand over around R1000 (about US$55 at the time of writing) for a post-paid electricity connection before even using a single unit of power, a number that has steadily increased over the years. Given this fixed cost alone could purchase the equivalent of around 400 kWh of usage on the same connection, many people, especially solar users, have switched to prepaid meter connections. Prepaid connections, typically have no or much lower fixed monthly connection costs, at the expense of higher per-unit pricing, which is of course, ideal for solar users.  An issue that tends to crop up fairly frequently with solar users that have existing or switch to prepaid meters is intermittent or non-functioning of the Customer Interface Unit (CIU). The CIU is the mobile /battery backed unit typically installed indoors that contains a display an...
Read more

Sunsynk 5 kW (5.5-K-SG01LP1) Hybrid Inverter - Technical Review

-
Image
Note: Since this is a review of a residential-type inverter, the context of this article is with the energy requirements of a residential solar/energy installation in mind. Welcome To Load Shedding The Sunsynk hybrid inverter was a small revelation when it began to gain prominence in the South African solar energy market circa 2019/2020.  South Africa was in the midst of a growing energy crisis that had begun in 2008. The government-owned energy parastatal, Eskom, was increasingly unable to meet energy demand, resulting in daily  energy cuts  euphemistically termed "load shedding" that operated on a graduated "stage"  schedule depending on the severity of the energy generation shortage. The greater the energy shortage, the higher the stage and more frequent the number of daily power cuts that lasted between two to four hours at a time. The growing energy generation crisis, shown in total number of hours of energy cuts.  Naturally, businesses and residents that c...
Read more