Tuesday, July 28, 2020

Trunk Based Development and Feature Flags for Continuous Delivery

Trunk Based Development is a branching model in which developers create short-lived feature branches and merge back into the “trunk” branch, often called as the master branch.

The guiding principals of Trunk Based Development

  • There is one “trunk” branch where developers merge their changes.
  • Developers should merge small changes as often as they can.
  • Merges must be reviewed, tested, and must not destroy the “trunk”.
  • All code in “trunk” must be release ready at all times.
  • Feature branches must be short-lived.
  • Keep your commit messages as concise as possible

Comparing Trunk Based Development to GitFlow


The Trunk Based Branching Model

The below model can be used for scaled teams, the development is done with short-lived feature branches, the changes are often merged to the “trunk”. For small teams, the developers can directly merge the changes to the “trunk” in small chunks.


Changes made in the release branches — snapshots of the code when it’s ready to be released — are usually merged back to trunk as soon as possible. One key benefit of the trunk-based approach is that it reduces the complexity of merging events and keeps code current by having fewer development lines and by doing small and frequent merges.

The developers should experienced enough to make this model successful, this model often creates conflicts if the changes are not reviewed and tested rigorously. Use this model if you are looking to push out a new product fast and want to iterate quickly.

Feature Development with Feature Flags

Trunk Based Development uses Feature Flags as a mechanism to manage new feature releases. A feature flag is simply a boolean condition that modifies the behavior of a component, module, or function in your application.

Following a Feature Flag pattern trades the simplicity of isolated branch workflows, such as GitFlow, in favor of flexible feature rollouts, continuous delivery, and application personalization.

Setting Up Feature Flags

A simple way to begin using feature flags is to maintain a single file containing your feature flags. Let us see how to manage the flags in Typescript with React application through a simple approach. The feature flags can also be managed through external tools like optimizel or launchdarkly

featureFlags.tsconst featureFlags = {
hellowordnewfeature: false
export function getFeatureFlag(key){
return featureFlags[key] || false;
//return feature based on the feature flag
import { getFeatureFlag } from "./featureFlags";
const createHelloWord = () => {
return createNewHelloWord()
return createOldHelloWorld()

Here the new feature is returned based on the flag “hellowordnewfeature”, if the flag is “true” then the new feature(createNewHelloWord) is returned else the old feature(createOldHelloWorld).

This TypeScript module(featureFlags.ts) can be extended to fetch the features from external or internal services.

Existing Feature Development with Feature Flags

Existing feature development with feature flags is slightly more complex but offers more flexibility for continuous delivery and personalization.

Small Incremental Change

If the proposed feature is a small incremental change, we can modify an existing code path to augment behavior. Take for example adding a new calculation for the total.

featureFlags.tsconst featureFlags = {
hellowordnewfeature: false,
export function getFeatureFlag(key){
return featureFlags[key] || false;
// before
const calculateTotal = (qty, val) => {
return qty * val
// after
const calculateTotal= (qty, val, tax) => {
return qty * val * tax
return qty *val

Large Modification

If the proposed feature is large, for example, we want to display a completely new TaxCalculator component, we would need to define a new code path and entry-point for that component.

featureFlags.tsconst featureFlags = {
hellowordnewfeature: false,
export function getFeatureFlag(key){
return featureFlags[key] || false;
TaxCalculator.tsximport { getFeatureFlag } from "./featureFlags";
import { TaxCalculatorOld, TaxCalculatorNew } from "./components";
const TaxCalculator = props => {
return <TaxCalculatorNew />
return <TaxCalculatorOld />

New Feature Development with Feature Flags

New feature development with feature flags is simpler than existing features. Since there are no existing code paths for your code to execute, this code path will be disabled by default while this feature is WIP.

The new feature development process with flags should look like this;

  • create a feature flag for your new feature
  • begin working on your code
  • ensure your flag is false before merging into master
  • merge your code frequently
  • when the feature is ready for release, remove the flag


Trunk based Development and Feature Flags together can be used for continuous delivery, delivering the features faster to market. Planning them carefully will allow you to quickly deliver the new business features to the system. The feature flags can also be managed through external tools like optimizel or launchdarkly, tools provide SDK to manage the features external to the applications.




Friday, July 3, 2020

How to access the local files externally through ngrok and python HTTP Server?

This tutorial explains how to share or access the local files externally through ngrok and Python http server.
I have the below two scenarios
  • a set of files that needs to be shared outside
  • share a simple website externally
The above scenarios can be achieved through Apache Server and external DNS configurations but require more configurations efforts.
  • ngrok free or paid version
  • Python latest version
Let us see how to enable the above scenarios through ngrok and python HTTP server with minimal configuration effort.
As a first step download ngrok(ngrok.com) for the required OS and extract the files
The ngrok allows you to expose a webserver running on your local machine to the internet. Just tell ngrok what port your web server is listening on.
On the free plan, ngrok’s URLs are randomly generated and temporary. If you want to use the same URL every time, you need to upgrade to a paid plan so that you can use the subdomain option for a stable URL. There are different paid plans they will provide some advance features like custom/reserved domains and multiple tunnels etc

How ngrok works

You download and run a program on your machine and provide it the port of a network service, usually a web server.
It connects to the ngrok cloud service which accepts traffic on a public address and relays that traffic through to the ngrok process running on your machine and then on to the local address you specified.

Python HTTP Server

Python standard library comes with an in-built webserver which can be invoked for simple web client server communication
The required port number can be assigned and the web server is accessed through this port
My system has python version 3.7.0 installed— “py -vi”
In the first scenario, i want to share some regular files externally
share files externally through ngrok and python http server
To start the HTTP server, cd to to the folder that should be shared(C:\Albin\blogData\demo\Share) through command prompt and execute the command “py -m http.server 80” — change the port number as required
share files externally through ngrok and python http server
Now the files are accessible through localhost
share files externally through ngrok and python http server

Let's now start ngrok to share this folder externally, cd to the folder where ngrok was extracted(C:\Albin\SW\ngrok-stable-windows-amd64)
Execute “ngrok.exe http 80”(80 is where python HTTP server running)
share files externally through ngrok and python http server
Now the external requests(http/https) are forwarded to localhost webserver through ngrok proxy domain
share files externally through ngrok and python http server

The local folders can be shared directly without a HTTP server through inbuilt ngrok file server. To share the local folder directly through ngrok , as a first step configure the authtoken to the ngrok

The authtoken can be retrieved through ngrok dashboard — the user should signup for a account , copy the command to set the authtoken by navigating to the dashboard.

Execute the command


Start the ngrok process — e.g ngrok http “file:///C:\Albin\blogData\demo\blogproject.blogproject


Now the files under the specific folder is accessible externally

Let us now see how to enable the second scenario, to access simple website externally, created a index.html file along with some test files into a folder(C:\Albin\blogData\demo\site), cd to the folder where the index.html and other files are located
share files externally through ngrok and python http server
Re-start the HTTP server, the pages are now accessible outside
share files externally through ngrok and python http server
The traffic can be monitored through the following URL —
share files externally through ngrok and python http server
The ngrok and python HTTP server can be used to share the local files externally without much effort and configurations.

Thursday, July 2, 2020

Geo Location Based Redirects with CloudFront and Apache | Redirect Web traffic Based on Country of Origin with CloudFront

This tutorial explain the approach to enable Geo Location based redirects with CloudFront and Apache.

Geo IP based redirection

Geo IP based redirection is the process of automatically redirecting a website visitor by their geolocation.

There are multiple options to enable the location based redirects in Apache, one of the option is using Geo IP database like MaxMind Geo IP database to map users’s IP to their location. Maxmind Geo IP database can be enabled through Apache module.

If you are using any of the CDN e.g CloudFront provides specific headers with request location, CloudFront will detect the user’s country of origin and pass along the county code to origin server in the CloudFront-Viewer-Country header. You can use this information to customize your responses e.g redirecting the users to specific URL based on origin country.


Website enabled with CloudFront CDN and Apache

CloudFront Configurations

As a first step white list the CloudFront-Viewer-Country header in Cloudfront distribution

Access <<CloudFront Distribution>> →Behaviors → <<Specific Behavior>>

Edit the behavior

Whitelist CloudFront-Viewer-Country header — the header with user’s country of origin will be sent to origin server(Apache) on every request.

CloudFront-Viewer-Country header will have the two letter country code based on the request origin.

Enable Apache Redirect

Let us now enable the required redirect configuration to virtualhost, add the below redirect rules to enable the the country specific redirects

<VirtualHost *:80>

ServerAdmin [email protected]
DocumentRoot "C:\opt\communique\dispatcher\cache"
ServerName test.albinsblog.com
ServerAlias localhost

RewriteEngine On

RewriteCond %{REQUEST_URI} ^/content/we-retail.html
RewriteRule ^.*$ https://test.albinsblog.com/content/we-retail/us/en.html [R=302,L]
RewriteCond %{REQUEST_URI} ^/content/we-retail.html
RewriteRule ^.*$ https://test.albinsblog.com/content/we-retail/it/it.html [R=302,L]
RewriteCond %{REQUEST_URI} ^/content/we-retail.html
RewriteRule ^.*$ https://test.albinsblog.com/content/we-retail/ca/en.html [R=302,L]
RewriteCond %{REQUEST_URI} ^/content/we-retail.html
RewriteRule ^.*$ https://test.albinsblog.com/content/we-retail/fr/fr.html [R=302,L]
<Directory />
Options Indexes FollowSymLinks Includes
# Set includes to process .html files
AddOutputFilter INCLUDES .html
AddOutputFilterByType INCLUDES text/html
AllowOverride None


I am using some VPN tool to initiate the connection from different origin country.

Connected the VPN to Canada

Now the user is redirected to Canada specific URL

The user is redirected to the country specific URL based on the users country of origin, CloudFront will detect the user’s country of origin and pass along the county code to origin server(Apache) in the CloudFront-Viewer-Country header. The Apache server redirect the user to the country specific URL’s based on the country code values in CloudFront-Viewer-Country header.

Friday, May 15, 2020

Error while creating the the new Maven projects - Caused by: java.lang.NoClassDefFoundError: org/apache/ivy/core/report/ResolveReport

Error while creating the new Maven projects - Caused by: java.lang.NoClassDefFoundError: org/apache/ivy/core/report/ResolveReport

I was getting the below exception while creating the AEM projects through Adobe Maven Arch Type 23, even the same issue was reported while generating the through Arch Type 22. 

mvn -e -B archetype:generate -D archetypeGroupId=com.adobe.granite.archetypes -D archetypeArtifactId=aem-project-archetype -D archetypeVersion=23 -D aemVersion=cloud -D appTitle="My Site" -D appId="mysite" -D groupId="com.mysite" -D frontendModule=general -D includeExamples=n -DappsFolderName=mysite

Enabled the flag -e to get more detailed errors - the below expection was thrown while executing the maven command

Number of foreign imports: 1
import: Entry[import  from realm ClassRealm[maven.api, parent: null]]


    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:169)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: java.lang.NoClassDefFoundError: org/apache/ivy/core/report/ResolveReport
    at java.lang.Class.getDeclaredMethods0 (Native Method)
    at java.lang.Class.privateGetDeclaredMethods (Class.java:2701)
    at java.lang.Class.getDeclaredMethods (Class.java:1975)
    at org.codehaus.groovy.reflection.CachedClass$3$1.run (CachedClass.java:84)
    at java.security.AccessController.doPrivileged (Native Method)
    at org.codehaus.groovy.reflection.CachedClass$3.initValue (CachedClass.java:81)
    at org.codehaus.groovy.reflection.CachedClass$3.initValue (CachedClass.java:79)
    at org.codehaus.groovy.util.LazyReference.getLocked (LazyReference.java:46)
    at org.codehaus.groovy.util.LazyReference.get (LazyReference.java:33)
    at org.codehaus.groovy.reflection.CachedClass.getMethods (CachedClass.java:250)

After a long struggle identified the issue was not specific to the arch type and caused by the corrupted local maven repository, the issue got resolved after removing the org folder folder from the maven repository(renamed the folder to org_bak)