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Blog - Page 9

Usable configuration with Git
27th July 2016

The configuration dilemma

As developers, almost every app we write has configuration. Often, that configuration should really be accessible to our less technical colleagues: feature flags, rate limits, deployment signoffs, and so forth.

However, these changes also need to be tracked and audited. “The app just broke. Did someone change the config?” “Quick, revert it to last week’s settings!”

As programmers, we know exactly the right tool for this: Text files in version control. They’re diffable, trackable and comprehensible, and if anything goes badly wrong we can dive in with a text editor.

The problem comes when we present this solution to our non-technical colleagues. “So, I open the terminal? And then I type git clone and a string of gibberish you made me memorise?”

It’s tempting to give up and say, “I’ll do it for you”. Developers end up as gatekeepers, with every change coming through us.

This isn’t great either. Years ago, I used to develop SMS-based services for a mobile carrier in south-east Asia. This was the bad old days, before Twilio and friends, and the carrier had to sign off on every minor UI change – often at the very last minute. I spent many late nights waiting for a meeting on the other side of the world to finish, just so I could change one line in a config file.

GitHub API to the rescue

We can fix this. With the GitHub API, we can build an app in minutes that empowers our colleagues to change configuration on their own – with all the power of Git’s versioning and auditing.

Here’s a simple app, hosted on Heroku (source at It has a configuration file (called config.json) that determines vital parameters such as the font and background colour.

Open in new tab

Here’s how I built an Anvil app to edit that configuration, with less than a dozen lines of code:

Getting the config

First, we need to grab the latest version of our config file:

self.gh_record = anvil.http.request("", json=True, username="abc", password="123")

Github returns some information about this file, and its content in base64:

  "name": "config.json",
  "encoding": "base64",
  "size": 67
  ...several other bits omitted...
  "content": "eyJ1cHBlcmNhc2UiOnRydWUsImZvbnQiOiJIZWx2ZXRpY2EiLCJiYWNrZ3Jv\ndW5kIjoiYmxhbmNoZWRhbG1vbmQifQ==\n",
  "sha": "bfb17ee5edf43a54f6756f032603872ca7dce320",

The content is what we care about:

self.item = json.loads(base64.b64decode(self.gh_record["content"]))

The decoded data looks like this:

  "background": "blanchedalmond",
  "font": "Helvetica",
  "uppercase": true

All we need now is to design our configuration interface. With Anvil’s data bindings, it’s all drag-and-drop - we can just specify which JSON key (in self.item) each text-box or check-box corresponds to. That’s all we need for a read-only interface:

See source code for this app
Committing our config

Now we have read-only access to our configuration, the next step is to save our changes. As we interact with the text-boxes and check-box, self.item is automatically updated.

Now we just push this data back to the server, with an HTTP PUT request to the same URL. All GitHub needs is the new content for the file, a commit message, and the previous SHA hash of this file:

new_record = {'content', base64.b64encode(json.dumps(self.item)),
              'message', 'Edit from the web'}
              'sha': self.gh_record["sha"]}

anvil.http.request("", method="PUT", data=new_record, json=True, username="abc", password="123")

And here’s the working app. Why not try changing some settings?

See source code for this app

Once you’ve saved your changes, scroll up and refresh the example app. Be patient - it may take a few seconds to re-deploy with the new config.

Increased security

OK, we’re not quite done. So far, we’re doing everything on the client side, which means everyone with the URL can access our authentication information! Even if we only give that URL out to people we (mostly) trust, it’s far too easy for it to end up in the wrong hands.

Instead, we’ll do our GitHub API calls on the server side, and expose only two functions to the client: save_config and load_config. All the rest is safely on the server, where the user can’t see it:

# This code runs on the server
def load_config():
  gh_record = anvil.http.request("", json=True, username="abc", password="123")

  return (gh_record['sha'], json.loads(base64.b64decode(gh_record['content'])))

def save_config(data, last_sha):
  new_record = {'content': base64.b64encode(json.dumps(data)),
                'message': 'Edit from the web',
                'sha': last_sha}
  r = anvil.http.request("", method="PUT", data=new_record, json=True, username="abc", password="123")

  return r['content']['sha']
Copy the final app to see its full source code

(In fact, I’ve been using this version of the code for all the example apps embedded in this blog post. I’m afraid wasn’t feeling generous enough to share my GitHub authentication tokens with anyone who can View Source. Sorry to disappoint anyone who tried.)

Job done.

There you have it - a secure, functional configuration editor, ready for our non-technical colleagues to use. You don’t need to know Git to use it, but it does have full tracing and history of every change.


#1: We don’t have to sacrifice the benefits of Git for our configuration, just in order to get a user-friendly admin interface. We can have both!

#2: The GitHub API is awesome.

#3: Anvil lets you build useful web apps very, very quickly.

Why not clone this example app, read its source code, and try it out yourself?

Version control and Anvil
11th July 2016

Git access for your apps

Rapid development is great, and Anvil lets you build web apps amazingly fast. But sometimes you need more. You need tracking, collaboration, code review, versioning. In short, you need source control.

Today, we’re announcing availability of Git access for your Anvil apps. It’s simple: each Anvil app is its own Git repository. Just clone the repository, and you can pull, push, edit and merge Anvil apps right from your workstation.

Now you can collaborate on multi-person teams, manage deployment and staging environments, and integrate Anvil into your code review process.

You can find everything you need to clone an app with Git in the Anvil app editor. Just select Version History from the Gear menu Gear Menu Icon, and click Clone with Git.

To learn more about Anvil, watch our video tutorial series. (Or, you can sign up and start building right away!)

Watch a tutorial

Anvil On-Site Installation
12th April 2016

Using Anvil behind your firewall

Anvil is, by default, a cloud-hosted service. This makes it incredibly easy to create web-apps that are live in the cloud, accessible from anywhere, and integrate with other cloud services.

If you’re in a corporate environment, your web app may need to access local resources. For example, you might want to use Anvil to query a database on your corporate network. For this, you will normally use the Anvil Uplink. This lets you securely give your Anvil app access to the relevant parts of your database:

The Anvil Uplink is available to all users, and does not store any data in the Anvil cloud. To learn more, watch our 4-minute video or read our documentation.

Sometimes, that's not enough.

Certain enterprise users, however, require more assurance. For example, organisations dealing with healthcare data may not transfer patient records to third-party services without special agreements.

For these users, we offer Anvil On-Site Installation. This allows you to develop and run your app entirely behind your corporate firewall, on servers you control:

An on-site Anvil installation requires no connection to the outside internet, giving you maximum assurance that your data is under your control.

Anvil On-Site Installation runs as a Docker container. It typically takes less than five minutes to get Anvil On-Site working on your network - and Anvil staff will be there to help you every step of the way.

If you want to run Anvil apps on your own network, please get in touch to find out more or arrange a free trial:

Arrange a trial

Introducing Anvil
20th February 2016

Making an interactive website should be easy, right?

Not so much. Let’s say you want a site to take orders for your new widget, or keep track of your customers, or schedule your local football league. Traditionally, you’ll need to know an alphabet soup of languages and technologies: HTML, CSS, JS, PHP, SQL - the list goes on. And that’s before we start on the complex frameworks required to make them usable.

This makes web development slow and complicated for professionals, difficult for other engineers, and entirely inaccessible for beginners.

We need to do better than this. So we built Anvil.

Web apps made simple

Anvil is a tool for making interactive websites in Python. Build your site with drag and drop, placing text, buttons, input boxes, images and more. Then double-click a button and write the Python that executes when that button is clicked.

You can make something really quick this way. Watch us build a page that greets you by name, in 45 seconds flat:

Want to try this yourself? Check out our tutorials

Simple built-in database

Anvil’s built-in database has a simple, spreadsheet-like interface for editing your data. Searching or editing it from your code is a no-nonsense Python statement. You can build a working database-backed to-do list app in five minutes - watch us do it!

If you already have a database, no problem - Anvil can connect to that too. (For those with special requirements, we even offer an on-site solution)

Use the rest of the web

No app is an island, and you shouldn’t have to build things from scratch. Anvil makes it easy for your apps to use services from the rest of the web:

Authenticate with Google login
Accept credit cards with Stripe
Store files in Google Drive
Store data in Google Sheets
Use local resources

You might want to use something that’s only available on your network, or your computer. Perhaps you want to use your company database, or special hardware, or files stored on your computer.

With Anvil, that’s a snap. Just import a library, mark the functions you want to call from Anvil, and away you go.

Watch us control a Raspberry Pi from the web in three minutes.

Try it out

Anvil is free for personal use, and we can’t wait to see what you will build with it. Why not sign up for free and try it out?

Build an app

Learn More

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