lunes, febrero 12, 2018

Repeatable Annotations in Java 8

With Java 8 you are able to repeat the same annotation to a declaration or type. For example, to register that one class should only be accessible at runtime by specific roles, you could write something like:

Notice that now @Role is repeated several times. For compatibility reasons, repeating annotations are stored in a container annotation, so instead of writing just one annotation you need to write two, so in the previous case, you need to create @Role and @Roles annotations.

Notice that you need to create two annotations, one which is the "plural" part of the annotation where you set return type of value method to be an array of the annotation that can be used multiple times. The other annotation can be used multiple time in the scope where it is defined and must be annotated with @Repeatable annotation.

This is how I did all the time since Java 8 allows to do it. But last week, during a code review my mate George Gastaldi pointed me out how they are implementing these repeatable annotations in javax.validation spec.  Of course, it is not completely different but I think that looks pretty much clear from point of view implementation since everything is implemented within the same archive and also, in my opinion, the name looks much natural. 

Notice that now everything is placed in the same archive. Since usually you only need to refer to @Role class, and not @Roles (now @Role.List) annotation you can hide this annotation as an inner annotation. Also in case of defining several annotations, this approach makes everything look more compact, instead of having of populating the hierarchy with "duplicated" classes serving the same purpose, you only create one.

Of course, I am not saying that the approach of having two classes is wrong, at the end is about preferences since both are really similar. But after implementing repeatable annotations in this way, I think that it is cleaner and compact solution having everything defined in one class.

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lunes, enero 08, 2018

Secret Rotation for JWT tokens

When you are using JSON Web Token (JWT), or any other token technology that requires to sign or encrypt payload information, it is important to set an expiration date to the token, so if the token expires, you can either assume that this might be considered a security breach and you refuse any communication using this token, or you decide to enable the token by updating it with new expiry date.

But it is also important to use some kind of secret rotation algorithm, so the secret used to sign or encrypt a token is periodically updated, so if the secret is compromised the tokens leaked by this key is less. Also in this way you are decreasing the probability of a secret being broken.

There are several strategies for implementing this, but in this post, I am going to explain how I implemented secret rotation in one project I developed some years ago to sign JWT tokens with HMAC algorithm.

I am going to show how to create a JWT token in Java.

Notice that what you need to do here is creating an algorithm object setting HMAC algorithm and set a secret that is used to sign and verify instance.

So what we need is to rotate this algorithm instance every X minutes, so the probability of breaking the secret, and that the broken secret is still valid, becomes very low.

So how to rotate secrets? Well, with a really simple algorithm that everyone (even if you are not a crypto expert) can understand. Just using time.

So to generate the secret, you need a string, in the previous example was secret String, of course, this is not so secure, so the idea is to compose this secret string by a root (something we called the big bang part) + a shifted part time. In summary the secret is <bigbang>+<timeInMilliseconds>

Bing bang part has no mystery, it is just a static part, for example, my_super_secret.

The interesting part is the time part. Suppose you want to renew secret every second. You only need to do this:

I am just putting 0s to milliseconds part, so if I run this I get something like:


Notice that although between second and third print, it has passed 50 milliseconds, the time part is exactly the same. And it will be the same during the same second.

Of course, this is an extreme example where the secret is changed every second but the idea is that you remove the part of the time that you want to ignore, and fill it with 0s. For this reason, first, you are dividing the time and then multiply by the same number.

For example, suppose that you want to rotate the secret every 10 minutes you just need to divide and multiply for 600000.

There are two problems with this approach that can be fixed although one of them is not really a big issue.

The first one is that since you are truncating the time if you want to change the secret every minute and for example, the first calculation occurs in the middle of a minute, then for just this initial case, the rotation will occur after 30 seconds and not 1 minute. Not a big problem and in our project, we did nothing to fix it.

The second one is what's happening with tokens that were signed just before the secret rotation, they are still valid and you need to be able to verify them too, not with the new secret but with previous one.

To fix this, what we did was to create a valid window, where the previous valid secret was also maintained. So when the system receives a token, it is verified with the current secret, if it passes then we can do any other checks and work with it, if not then the token is verified by the previous secret. If it passes, the token is recreated and signed with the new secret, and if not then obviously this token is invalid and must be refused.

To create the algorithm object for JWT you only need to do something like:

What I really like about this solution is:

  • It is clean, no need for extra elements on your system.
  • No need for triggered threads that are run asynchronously to update the secret.
  • It is really performant, you don't need to access an external system.
  • Testing the service is really easy.
  • The process of verifying is responsible for rotating the secret.
  • It is really easy to scale, in fact, you don't need to do anything, you can add more and more instances of the same service and all of them will rotate the secret at the same time, and all of them will use the same secret, so the rotating process is really stateless, you can scale up or down your instances and all instances will continue to be able to verify tokens signed by other instances.

But of course there are some drawbacks:

  • You still need to share a part of the secret (the big bang part) to each of the services in a secure way. Maybe using Kubernetes secrets, Vault from Hashicorp or if you are not using microservices, you can just copy a file into a concrete location and when the service is up and running, read the big bang part, and then just remove it.
  • If your physical servers are in different time zones, then using this approach might be more problematic. Also, you need that the servers are more or less synchronized. Since you are storing the previous token and current token, it is not necessary that they are synced in the same second and some seconds delay is still possible without any issue.

So we have seen a really simple way of rotating secrets so you can keep your tokens safer. Of course, there are other ways of doing the same. In this post, I just have explained how I did it in a monolith application we developed three years ago, and it worked really well.

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miércoles, enero 03, 2018

Cloud Native Applications with JWT

A native cloud application is an application that is developed for a cloud computing environment.

There is no specific answer to the question "what is a cloud-native application" but different concepts that must be met. 

One of the most important in my opinion is the ability to scale up and down at a rapid rate. And this means that our applications cannot have any state on each of the servers since if one server goes down or is scaled down, then the state stored in that server will be lost.

This is very well summarized at where it is explained with a shopping cart example. In monolith approach, you store the products of the shopping cart in a server session, if the server went down then all products of shopping cart were lost as well. In a cloud-native app, where server instances can be scaled up and down quickly, it is important to not have this stateful behavior on your services and design them to be stateless.

There are different approaches to achieve this goal of implementing a stateless architecture but they can be summarized into two categories:
  • Use a distributed in-memory key/value data store like Infinispan.
  • Use a token which acts as a session between client and server using for example JWT.
In this post, I am going to introduce you the later approach.

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object.  

This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret using HMAC or a public/private key pair using RSA.

JSON Web Tokens consist of three Base64Url strings separated by dots which are: Header.Payload.Signature

So the idea basic idea for implementing stateless architecture on backend using JWT is the next one:
  1. When the user adds the first product, the backend service generates a new JWT token with the product added and sent it back to the frontend.
  2. When the user adds a new product, it sends the product to add and also the JWT token that was sent before by backend.
  3. Then the backend verifies that the token has not been modified (verifying the signature), then it gets the products from JWT payload added previously and add the new one to the list. Finally, it creates a new token with previous and new products and it sent it back to the frontend.
  4. The same process is repeated all the time.

So as you can see, now it is not necessary to maintain any state or add any new database service on backend side, you just need to sent back and forward the JWT token with the products inside.

I have recorded a video of a simple shopping cart example where I show the stateless nature of the solution. It can be seen at:

Also if you want to check the project that I used for recording you can take a look at

Notice that this is just a simple post so you can get the basic idea. But you need to take into consideration next things to use it in production:
  1. Use HTTPS instead of HTTP
  2. JWT just signs the token, if you want extra protection apart from HTTPS, use JWE to encrypt the payload of JWT token as well.
  3. Fingerprinting the token to avoid any man-in-the-middle attack and use these parameters as authentication parameters for the token.
  4. JWT can be used for passing authentication and authorization things as well.
You can watch my talk at JavaZone where I introduce some of these techniques:

The good part of JWT approach is that it simplifies a lot the deployment of the service, you don't need to deploy or configure any other distributed database to share the content across the cluster, which minimizes the problems related to the network for communicating to the distributed database or misconfiguring of any of the nodes.

The drawback is that the client needs to be aware to receive and sent back the token and deal with it. In backend side, you need to sign and verify every token all the time.

Note that this approach might work in some cases and might get into some troubles in others (for example if there are parallel connections to backend all of them modifying the token). This post just shows an example of how I implemented this stateless thing in a project with specific requirements, but in other cases it might be wrong to do it. A real shopping cart implementation would have some problems, but for the sake of simplicity and having a business model that everyone undertands, I decided to implement it in this way.

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martes, enero 02, 2018

Writing end to end test for a microservices architecture

UPDATE: I was not really sure if I should call this post with e2e tests since I knew it can get some confusions, but I couldn0t think about any other name. After reading I can be sure that what I am describing here is how to do Narrow Integration Test.

One of the main aspects of microservices architecture is that the application is formed as a collection of loosely coupled services each one deployable independently and communicated each other with some kind of light protocol.

It is because of microservices architecture is a distributed system that makes writing end to end tests really hard. Suppose next simple example provided by Red Hat as an example of microservices architecture (

Now suppose that you want to write an end to end test for Cart Service. You will quickly see that it is not easy at all, let me enumerate some of the reasons:

  • Cart Service needs to know how to boot up Pricing Service, Catalog Service, and MongoDB (and if you want to involve the front-end as well then Coolstore GW and WebUI).
  • Cart Service needs to prepare some data (fixtures) for both of external services.
  • You communicate with services using a network. It might occur that some tests fail not because of a real failure but because of an infrastructure problem or because the other services have any bug. So the probability of these tests become flaky and start failing not because any changed introduced in current service is higher.
  • In more complex cases running these tests might be expensive, in terms of cost (deploying to the cloud), time (booting up all the infrastructure and services) and maintenance time.
  • Difficult to run them in developer machine, since you need all the pieces installed on the machine.

For this reason, the end to end tests is not the best approach for testing a microservice, but you still need a way to test from the beginning to the end of the service.

It is necessary to find a way to "simulate" these external dependencies without having to inject any mock object. What we need to do is cheat the service under test so it really thinks it is communicating with the real external services, when in reality it is not.

The method that allows us to do it is Service Virtualiztion.  Service virtualization is a method to emulate the behavior of component applications such as API based.

You can think about service virtualization as mocking approach you used to implement in OOP but instead of simulating at the object level, you simulate at the service level. It is mocking for the enterprise.

There are a lot of service virtualization tools out there, but in my experience, in the JVM ecosystem, one of the tools that work better is Hoverfly.

Let's see how an "end-to-end" test looks like for Cart Service.

This service is implemented using Spring Boot, so we are using Spring Boot Test framework. The important part here is that the URL where Catalog service is deployed is specified by using CATALOG_ENDPOINT property.  And for this test, it is set to catalog.

The next important point is the Hoverfly class rule section. In that rule next things are specified:
  1. An Http proxy is started before the test and all outgoing traffic from JVM is redirected to that proxy.
  2. It records that when a request to host catalog is done and the path is /api/products it must return a success result with given json document.

The test itself just uses TestRestTemplate (it is a rest client) and validates that you can add some elements to the cart.

Notice that you don't need to configure where the Http proxy is started or configure any port because Hoverfly automatically configures JVM network parameters so any network communication goes through Hoverfly proxy.

So notice that now you don't need to know how to boot up Catalog service nor how to configure it with correct data.

You are testing the whole service within its boundaries, from incoming messages to outgoing messages to other services, without mocking any internal element.

Probably you are wondering "What's happening in case of current  service has also a dependency on a database server?"

In this case, you do as usual since the service itself knows which database server is using and the kind of data it requires, you only need to boot up the database server, populate required data (fixtures) and execute tests. For this scenario I suggest you using Arquillian Cube Docker to bootup database service from a Docker container so you don't need to install it on each machine you need to run tests and Arquillian Persistence Extension for maintaining the database into a known state.

In next example of rating service, you can see briefly how to use them for persistence tests:

With this approach, you are ensuring that all inner components of the service work together as expected and avoiding the flakiness nature of end to end tests in microservices.

So end to end tests in any microservice is not exactly the same of an end to end test in a monolith application, you are still testing the whole service, but just keeping a controlled environment, where test only depends on components within the boundary of service.

How contract tests fit on this? Well actually everything showed here can be used in consumer and provider side of contract testing to avoid having to boot up any external service.  In this way, as many authors conclude, if you are using contract tests, these are becoming the new end to end tests.

viernes, diciembre 29, 2017

Java Champion

Before Christmas, I received the good news that I become a Java Champion. And then many memories came to my mind. My first computer, the ZX Spectrum that my parents bought me when I was 6, the first game I had, Desperado (  from TopoSoft. All programs that I copied from books in Basic language, all modifications I did and of course all the "pokers" that I copied from magazines to have infinite lives in games.

After that, it started the PC era, where I remember creating many "bat" files for having different memory configurations for playing games, editing saved files with Hex editors to have millions of resources and the appearance of Turbo C in my computer.

Finally, the internet era, that for me started in 1997, and my first browser which it was Netscape. What good old time, and then my first web page and JavaScript.

And this moves me towards the key point, I think it was at 1999 or 2000, I bought a magazine which it came with a CD-ROM with Java 1.2 there, I installed and I started programming in Java without IDE until today.

Probably this is the life of many of developers that were born in the 80s. 

But this is only "scientific" facts, not feelings. These days I have been thinking about the feelings I had, what ruled to me all this time, and it came to my mind the opening theme of one of my favorite TV program called "This is Opera". Exactly the same words can be applied in my case for programming/computing/Java.

I cannot finish without thanking all the people who I met over the globe during conferences, starting with Dan Allen (the first one I met at a conference), all Arquillian team, Tomitribe team with David Belvins at head), Asciidoctor community, Barcelona JUG guys and a lot of people, organizers, attendees, .... every one thank you so much for being there.

Of course, all the workmates I had in University (La Salle), in Aventia, Grifols (thanks to Erytra team, I enjoyed so much during all years I was there), Everis, Scytl, CloudBees (LLAP to Jenkins) and finally Red Hat, a company that I really love and I feel like home.

Last but not least my family who has been there all the time.

Next year I will continue posting more posts, contributing more to open source projects and of course going to speak to as many events as possible.

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Caminante son tus huellas el camino y nada más: caminante, no hay camino se hace el camino al andar (Caminante No Hay Camino - Joan Manuel Serrat)

miércoles, octubre 25, 2017

Adding Chaos on OpenShift cluster

Pumba is a chaos testing tool for Docker and Kubernetes (hence OpenShift too). It allows you to add some chaos on containers instances such as stopping, killing or removing containers randomly. But it also adding some network chaos such as delaying, packet loss or re-ordering.

You can see in next screen recording how to add Pumba on OpenShift cluster and add some chaos on it.

The security calls that you need to run before deploying Pumba are the next ones:

Also the Kubernetes script to deploy Pumba in OpenShift is:

I have sent a PR to upstream Pumba project with this file but meanwhile is not accepted you can use it this one.

I'd like to say thank you to Slava Semushin and Jorge Morales for helping me on understanding the OpenShift security model.

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martes, octubre 24, 2017

Testing Code that requires a mail server

Almost all applications has one common requirement, they need to send an email notifying something to a registered user. It might be an invoice, a confirmation of an action or a password recovery. How to test this use case might be challenging, using mocks and stubs are ok for unit tests, but having a component test that tests the whole stack. 

In this post I am going to show you how Docker and MailHog, can help you on testing this part of code.

MailHog is  super simple SMTP server for email testing tool for developers:
  • Configure your application to use MailHog for SMTP delivery
  • View messages in the web UI, or retrieve them with the JSON API
  • Optionally release messages to real SMTP servers for delivery
  • Docker image with MailHog installed
Notice that since you can retrieve any message sent to mail server using JSON API, it makes really simple to validate if the message has been really delivered and of course assert on any of message fields.

Arquillian Cube is an Arquillian extension that can be used to manager Docker containers in your tests. To use it you need a Docker daemon running on a computer (it can be local or not), but probably it will be at local.

Arquillian Cube offers three different ways to define container(s):
  • Defining a docker-compose file.
  • Defining a Container Object.
  • Using Container Object DSL.
In this example I am going to show you Container Object DSL approach, but any of the others works as well.

To use Container Object DSL you simply need to instantiate the ContainerDslRule (in case you are using JUnit Rules) or use Arquillian runner in case of using JUnit, TestNG or Spock. You can read more about Container Object DSL at

As an example of definition of Redis container:

When running this test, Redis Docker image is started, tests are executed and finally the Docker instance is stopped.

So let's see how to do the same but instead of Redis using Mailhog Docker image.
It is important to notice that ContainerDslRule is a generic class that  can be extended to become more specific to a concrete use case. And this is what we are going to do for Mailhog.

First of all we need to create a class extending from ContainerDslRule, so everything is still a JUnit rule, but a customized one. Then we create a factory method which creates the MailhogContainer object, setting the image name and the binding ports. Finally an assertion method is used to connect to Rest API of Mailhog server to check if there is any message with given subject.

Then we can write a test using this new rule.

This test just configures MailService class with Docker container configuration, it sends an email and finally it delegates to container object to validate if the email has been received or not.

Notice that putting everything into an object makes this object reusable in other tests and even in other projects. You can create an independent project with all your custom developed container objects and just reuse them importing them as test jar in hosted project.


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'Cause I'm kind of like Han Solo always stroking my own wookie, I'm the root of all that's evil yeah but you can call me cookie (Fire Water Burn - Bloodhound Gang)