Practical Software Architecture: Moving from System Context to Deployment

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Spring has long been a central place to go for frameworks enabling quick and easy JVM-based software development. Their Spring Cloud specialized section includes integrations with a lot of cloud infrastructure, including the above mentioned Netflix libraries among many others. This service mesh, written by Buoyant, was released to the open source world early in It runs as a sidecar and acts as a proxy between your services. It provides you with: load balancing, circuit breaking, service discovery, dynamic request routing, HTTP proxy integration, retries and deadlines, TLS, transparent proxying, distributed tracing, and instrumentation.

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As a sidecar application, it can be run once per service or once per host — so if you run multiple services per host, you can save on process overhead with Linkerd. They boast a couple of very well known names on their used by list. Interestingly, you can integrate Linkerd with Istio covered below. I am unclear what the benefits of this are, but a surface reading says there may be something there.

In December , almost two years after Linkerd, Buoyant released another service mesh specifically for Kubernetes clusters. They took their lessons learned, and are creating Conduit with the intention of being an extremely lightweight service mesh. The Conduit tooling works in tandem with the Kubernetes tooling to inject itself into your cluster. Once injected, most of the work happens behind the scenes through proxying and the use of standard Kubernetes service naming schemes. It claims good end-to-end visibility, but I do not see good screenshots of that, and have not yet tested it out myself.

A big caution here is the Alpha status and the extremely new creation— February They have published a Roadmap to Production with an insight of where they are going. Istio is a service mesh which came to us in May of Internally they are using Envoy covered next. They have instructions for deploying on top of Kubernetes, Nomad, Consul, and Eureka.

Ingress and Egress traffic is afforded the same feature set. Automatic metrics, logs, and traces are available quickly through included visualization tools. They also enable infrastructure level, run-time routing of messages based on content and meta information about the request. The downside is it is very young and restricted to specific deployment environments — though there is some documentation that may help you deploy in other environments using manual methods.

Istio uses iptables to transparently proxy network connections through the sidecar — in the Kubernetes world this is truly transparent to you, but in other environments, you are involved in making that work. On the upside, the security feature set feels mature and well thought out. All egress connections are, by default, denied until explicitly permitted — and that is refreshing! You protect your services within your mesh the same way you protect it at the ingress and Egress — nice!

The out-of-the-box visualization of your services as a network diagram and various per-service metrics provides you immediate observability into your environment. Large-scale deployments will likely need to own moving this into larger deployments, but as a getting started environment it is very nice. Originally built by Lyft, but released after Linkerd in , this one has the appearance of being the most mature. It was built to support running a single service or application as well as supporting a service mesh architecture.

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That said, Envoy is not a full-service mesh as it only provides the data plane and you must manage the Envoy processes yourself or use Istio which, by default, uses the Envoy proxy. A quick look through the documentation shows a healthy list of features, including filters, service discovery, health checking, load balancing, circuit breaking, rate limiting, TLS, statistics, tracing, logging, and much more. I am extremely excited to sit down with each of these existing technologies and give them a thorough run-through. With the sheer amount of functionality they already provide, I would be woefully remiss to not understand them and include them as the basis for whatever microservices macro-architecture I support in my organization.

Building all of this functionality from scratch, and not taking advantage of the great work already done by so many fine, brilliant individuals would be a crime. I would rather my organization spend its time on the services and functionality that makes them money — or, if we must extend more functionality to the macro-architecture infrastructure, spend that time contributing back to one of these projects. Utilizing one of these service meshes will require us to understand it extremely well. We must be able to discern the implications it has upon our macro-architecture, and we must document those very carefully into our macro-architecture.

Oh yes, even if you choose a service mesh, you must still write down a macro-architecture for your microservices infrastructure. These service meshes are only providing you an immense jump start, and, in some cases, answering some of the questions for you. It has been an exciting time for me to get back to my very technical roots and dig deeper into modern architecture concepts through microservices.

I look forward to continuing this journey, and I hope to hear from any of you who have done so and may have tips for me that I had not thought to include here. Thank you all for your attention, and I hope you got something out of this article. I would like to close with a listing of the books I recently read in my quest for knowledge, one that I am currently reading, and two that I plan to read based on recommendations in other books and by multiple experts in software architecture.

A great introduction to the world of microservices with a strong focus on the broad spectrum of requirements necessary to enter into this world. Richard starts with practical definitions and direction on how to build microservices followed by an overview of what it takes to run microservices. This book provides a good understanding of messages as transport, pattern matching for routing, and the large effort monitoring and measuring your environment will be.

Warning: The author spends the first third of the book being rather derogatory towards any non-microservices approach to development. Read past that and he does have a good book. This book is broken up into logical sections. The first two give a lot of repetitive background information on microservices presenting what they are, are not, and when you should and should not use them. There is a severe lack of commas in the book, which sometimes trips you up, but the material is very good.

Part 3 turned this book into a complete winner for me when he began covering very specific pieces of information. The following books are currently in my queue to read based on recommendations in the previous books and also by experts in software architecture. Martin Fowler is one such expert who quickly rose to the top in my searching and reading. His website is an invaluable resource as well. As I said in the opening, I have been on this mission for a couple of months.

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If you are interested in seeing the progression of my journey and possibly gain more insight into some of these topics, please peruse my earlier investigative posts:. Learn Forum News. Tweet this to your followers. I have read and learned. Now it is time to take those first steps into the world of Microservices. First, for you, I document what I have learned and discovered thus far. Complexity comes from low cohesion and high coupling. Microservices provides the structure to keep that at bay. This is a great lead-in to the next section… Microservices: High-Level Requirements The Macro An environment which supports microservices fundamentally needs a set of baseline requirements to ensure some level of sanity.

The macro-architecture is one part provided infrastructure and one part policy requirements for all microservices. Choose wisely what you leave out of your macro-architecture. For every choice you allow the individual development teams to make, you must be willing to live with differing decisions, implementations, and operational behaviors. Logging It is vital to monitor your microservices in production. This implies that the macro-architecture should strongly consider including the following: A logging service for centralized logging. This can be the Elastic Stack , Slack , Graylog , and others of their ilk.

Part of your infrastructure can be one of these services, and a guarantee that each host in the environment will be configured to transfer log files on behalf of each service. Definition of trace IDs to enable the location of all logs across all microservices handling a single external request. The concept here is that, for every external request coming into your microservices, you generate a unique ID, and that ID is passed to any internal microservices calls used to handle that request.

Thus through a search for a single trace ID, you can find all microservices calls resulting from a single external access.

Base formatting requirements for server, service, instance, timestamp and trace IDs. Some macro-level data points include: The volume of messages, failures, successes, retries, and drops. The latency of requests. The ratio of received messages to sent messages. Status of circuit breakers. And more. Much, much more. Communication Mechanisms Microservices should have some level of control in how they implement their interfaces.

Persistence: Database, NoSQL, and so on A microservices architecture completely isolates each microservice from the rest. Here are some options you can look to include in the macro-architecture: One or more data storage services including an SQL based relational database and a NoSQL storage system. These provided data storage services should include built-in backups. In this scheme, the operations team providing the storage service are responsible for its operation.

If you allow the microservices to bring their own persistence, you should have strict policy requirements for backups and disaster recovery. Think about off-site backups, recovery time, fail-over time, and so on. Moreover we will illustrate how this process much faster and more holistically brings product requirements to the table. Target audience would be any person focussing on early stage product development. This includes programmers, project managers, UX-designers, UI-designers etc. Federico Lozano: Fede is Asst. Matilde Bisballe: Matilde is currently a Ph.

Her focus is understanding the skills needed in the early stages of product design with especially focus on prototypes and the pre-choices the facilitator makes when facilitating such processes. At the moment she is working on how one can prototype and improve user-experiences of smart-products by exploring different types of shape-changing interfaces. Finding the right scope for product development in order to build innovative products that customers want is crucial for success. Continuous exper-imentation is an important means to steer development towards rapid value creation and to avoid unnecessary development efforts.

Insights from such experiments can directly influence frequent iterative deliveries. Continuous experimentation helps companies to gain competitive advantage by reducing uncertainties and rapidly finding product roadmaps that work. However, defining a product strategy in a testable way and running the right experiments in an effective way is hard. Setting up experiments wrong can lead to false results and wrong business decisions. Target audiences are product managers, innovation managers, startup founders, business people, software developers, and IT consultants.

He regularly teaches product management courses and helps companies to develop innovation capabilities and new digitally-enabled products and services. He specializes in software engineering, in particular data- and value-driven software development, product management, agile engineering, and startups.

Results are documented in five books and more than refereed publications. Software security is about creating software that keeps performing as intended even when exposed to an active attacker. Secure software engineering is thus relevant for all software, not only security software. This tutorial will provide a brief introduction to the core principles of software security, and then go into specifics of threat modeling using data flow diagrams, attack trees and misuse cases.

We will then introduce Protection Poker, a tool for risk estimation to be used as part of the sprint planning meeting. Attendees will try out playing Protection Poker on a case related to the previous presentations. Target audiences are developers in general. His research interests include software security, security in cloud computing, and security of critical information infrastructures. He is vice chairman of the Cloud Computing Association cloudcom.

Her research interests include software security, cyber insurance and security in smart grids. Risk-based testing RBT is a testing approach which considers risks of the software product as the basis to support decisions in all phases of the test process. Risk-based testing has a high potential to improve the software test process as it helps to optimize the allocation of resources and provides decision support for the management. An adequate test strategy plays a key role in increasing test effectiveness and efficiency in terms of balancing product quality with cost and time-to-market.

Establishing a risk-based testing approach and its integration into an existing test process is a challenging task due the lack of concrete guidelines and empirical evidence on success criteria. In this tutorial we present the concept of risk in software testing as well as a practical approach for developing a risk-based test strategy.

The tutorial is based on results from previous research and studies investigating the introduction of risk-based testing in large organizations as well as the application of risk in testing in small and medium enterprises. Intended learning objectives include insights into the benefits and challenges of risk-based testing in practice, knowledge about a process for risk-based test strategy development and refinement, and an overview of open research issues.

Target audiences are both practitioners test managers, test analysts, testers and researchers. Michael Felderer is a professor at the University of Innsbruck, Austria. He holds a habilitation and a PhD degree in computer science. He has over 15 years of experi- ence in software engineering research and technology transfer. His research interests include software testing, security testing, requirements engineering, quality management, software processes as well as empirical software engineering. Michael is also a senior consultant for QE LaB Business Services, where he transfers his research results into practice and a regular speaker on industrial conferences.

He has over 15 years of experience in software engineering research and technology transfer. His research interests include software testing, quality manage- ment, and empirical software engineering. He holds a M. In many industries there is dual pressure on both being more agile and adaptive to changing requirements at the same time as being compliant with process standards like ASPICE and ISO These standards have not been adapted to agile development, and many of the underlying assumptions are based on a waterfall model.

We should assign a logically complete task to each module. The module is logically complete when it can be separated from the rest of the system and placed into another application. The interface design is extremely important. The interfaces also define the coupling between modules. In general we wish to minimize the bandwidth of data passing between the modules yet maximize the number of modules. Of the following three objectives when dividing a software project into subtasks, it is really only the first one that matters.

We will illustrate the process of dividing a software task into modules with an abstract but realistic example. The overall goal of the example shown in Figure 7. The organic light emitting diode OLED could be used to display data to the external world. Notice the typical format of an embedded system in that it has some tasks performed once at the beginning, and it has a long sequence of tasks performed over and over. The left side of Figure 7. The linear approach to this program follows closely to linear sequence of the processor as it executes instructions.

This linear code, however close to the actual processor, is difficult to understand, hard to debug, and impossible to reuse for other projects. Therefore, we will attempt a modular approach considering the issues of functional abstraction, complexity abstraction, and portability in this example. The modular approach to this problem divides the software into three modules containing seven subroutines. In this example, assume the sequence Step4-Step5-Step6 causes data to be sorted.

Notice that this sorting task is executed twice. A complex software system is broken into three modules containing seven subroutines. Functional abstraction encourages us to create a Sort subroutine allowing us to write the software once, but execute it from different locations.

Complexity abstraction encourages us to organize the ten-step software into a main program with multiple modules, where each module has multiple subroutines. For example, assume the assembly instructions in Step1 cause the ADC to be initialized.

Therefore, each well-defined task is defined as a separate subroutine. The subroutines are then grouped into modules. The complex behavior of the ADC is now abstracted into two easy to understand tasks: turn it on, and use it. Again, at the abstract level of the main program, understanding how to use the OLED is a matter knowing we first turn it on then we transmit data.

The math module is a collection of subroutines to perform necessary calculations on the data. In this example, we assume sort and average will be private subroutines, meaning they can be called only by software within the math module and not by software outside the module. The OLED device is used in this system to output results. The modular approach performs the exact same ten steps in the exact same order. However, the modular approach is easier to debug, because first we debug each subroutine, then we debug each module, and finally we debug the entire system.

The modular approach clearly supports code reuse. For example, if another system needs an ADC, we can simply use the ADC module software without having to debug it again. Observation: When writing modular code, notice its two-dimensional aspect. Down the y-axis still represents time as the program is executed, but along the x-axis we now visualize a functional block diagram of the system showing its data flow: input, calculate, output. The previous section presented fundamental concepts and general approaches to solving problems on the computer.

In the subsequent sections, detailed implementations will be presented. Decision making is an important aspect of software programming. Two values are compared and certain blocks of program are executed or skipped depending on the results of the comparison. In assembly language it is important to know the precision e. It takes three steps to perform a comparison. You begin by reading the first value into a register. If the second value is not a constant, it must be read into a register, too. The second step is to compare the first value with the second value. The last step is a conditional branch.

Observation: Think of the three steps 1 bring first value into a register, 2 compare to second value, 3 conditional branch, bxx where xx is eq ne lo ls hi hs gt ge lt or le. The branch will occur if first is xx second. In Programs 71 and 7. Program 7. However, it does matter if they are 8-bit or bit. Assembly code. GEqual7 ;. GNotEqual7 ;. Conditional structures that test for equality this works with signed and unsigned numbers. When testing for greater than or less than, it does matter whether the numbers are signed or unsigned. In each case, the first step is to bring the first value in R0; the second step is to compare the first value with a second value; and the third step is to execute an unsigned branch Bxx.

The branch will occur if the first unsigned value is xx the second unsigned value. GGreater7 ;. GGreaterEq7 ;. GLess7 ;.

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GLessEq7 ;. A conditional if-then is implemented by bringing the first number in a register, subtracting the second number, then using the branch instruction with complementary logic to skip over the body of the if-then. If-Then Statement - The statements inside an if statement will execute once if the condition is true. If the condition is false, the program will skip those instructions. Choose two unsigned integers as variables a and b, press run and follow the flow of the program and examine the output screen.

You can repeat the process with different variables. Example 7. In other words, we will force G1 into the range 0 to Solution : First, we draw a flowchart describing the desired algorithm, see Figure 7. To implement the assembly code we bring G1 into Register R0 using LDRB to load an unsigned byte, subtract 50, then branch to next if G1 is less than or equal to 50, as presented in Program 7.

We will use an unsigned conditional branch because the data format is unsigned. Flowchart of an if-then structure. An unsigned if-then structure. Write C code that executes the function isTen , if N is equal to Write C code that executes the function isEqual if H1 equals H2. In each case, the first step is to bring the first value in R0; the second step is to compare the first value with a second value; and the third step is to execute a signed branch Bxx. The branch will occur if the first signed value is xx the second signed value.

Similar to Program 7. Write C code that executes the function isNeg , if N is negative. Common error: It is an error to use an unsigned conditional branch when comparing two signed values. Similarly, it is a mistake to use a signed conditional branch when comparing two unsigned values. Observation: One cannot directly compare a signed number to an unsigned number. The proper method is to first convert both numbers to signed numbers of a higher precision and then compare.

Redesign the Example 7. Solution : We can use the same flowchart shown previously in Figure 7. The way to compare two values is to subtract them from each other and check if that subtraction resulted in a positive number, zero, or negative number. If the subtraction yields a zero, then the numbers are obviously equal and the Z bit will be set. If it is positive, that means the first value is bigger than the second value and the N bit will be 0.

If it is negative, then the first value is smaller than the second one and the N bit will be 1. The CMP instruction subtracts 50 from R0 but doesn't save the result, it just sets the condition codes. The BLE uses the condition codes to branch to next if G1 is less than or equal to 50, as presented in Program 7. However, we will use a signed conditional branch BLE because the data format is signed..

BLE is a signed branch. Notice that the C code for Program 7. This is because the compiler knows the type of variables G1 and G2; therefore, it knows whether to utilize unsigned or signed branches. Unfortunately, this similarity can be deceiving. When writing code whether it be assembly or C, you still need to keep track of whether your variables are signed or unsigned. Furthermore, when comparing two objects, they must have comparable types.

However, I recommend that you do not compare a signed variable to an unsigned variable. When comparing objects of different types, it is best to first convert both objects to the same format, and then perform the comparison. Conversely, we see that all numbers are converted to 32 bits before they are compared.

This means there is no difficulty comparing variables of differing precisions: e. We can use the unconditional branch to add an else clause to any of the previous if then structures. A simple example of an unsigned conditional is illustrated in the Figure 7. Once at high, the software calls the isGreater subroutine then continues. After executing the isLessEq subroutine, there is an unconditional branch, so that only one and not both subroutines are called. If-then-else - If statements can be expanded by an "else" statement.

If the condition is false, the program will execute the statements under the "else" statement. Choose two unsigned integers as variable a and b, press run and follow the flow of the program and examine the output screen. The format is. Expr2 : Expr3. The first input parameter is an expression, Expr1 , which yields a Boolean 0 for false, not zero for true. Expr2 and Expr3 return values that are regular numbers. The selection operator will return the result of Expr2 if the value of Expr1 is true, and will return the result of Expr3 if the value of Expr1 is false. The type of the expression is determined by the types of Expr2 and Expr3.

If Expr2 and Expr3 have different types, then promotion is applied. The left and right side perform identical functions. If b is 1 set a equal to 10, otherwise set a to 1. A 3-wide median filter can be designed using if-else conditional statements. Write C code that changes N to if N is initially greater than Switch statements provide a non-iterative choice between any number of paths based on specified conditions.

They compare an expression to a set of constant values. Selected statements are then executed depending on which value, if any, matches the expression. The expression between the parentheses following switch is evaluated to a number and compared one by one to the explicit cases. The break causes execution to exit the switch statement. The default case is run if none of the explicit case statements match.

The operation of the switch statement performs this list of actions:. If Last is equal to 10, then theNext is set to 9. If Last is equal to 9, then theNext is set to 5.

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If Last is equal to 5, then theNext is set to 6. If Last is equal to 6, then theNext is set to If Last is not equal any of the above, then theNext is set to When using break , only the first matching case will be invoked. In other words, once a match is found, no other tests are performed. The body of the switch is not a normal compound statement since local declarations are not allowed in it or in subordinate blocks. Assume the output port is connected to a stepper motor, and the motor has 24 steps per rotation. Calling OneStep will cause the motor to rotate by exactly 15 degrees.

This example of a switch statement shows that the multiple tests can be performed for the same condition. Quite often the microcomputer is asked to wait for events or to search for objects. Both of these operations are solved using the while or do-while structure. Assume Port A bit 3 is an input. The operation is defined by the C code. Flowchart of a while structure. Execute Body over and over bit 3 of G1 is high.

If bit 3 is low then the body of the while loop is skipped. In this way, the body is executed repeatedly until Port A bit 3 is low. AND R0, 0x08 ; test bit 3. Body ;. Observation: The body of a while loop may execute zero or more times, but the body of a do-while loop is executed at least once. One of the conventions when writing assembly is whether or not subroutines should save registers. Conversely, if a subroutine wishes to use R4 through R11, it will preserve the values using the stack. Similarly, if the subroutine wishes to use LR e.

This means address pointers R4 and R5 only need to be set once in Program 7. However, since the variables themselves are held in RAM and may therefore be changed by some other piece of code, it does make sense to reload the values of the variables each time through the loop. Write C code that calls the function body over and over as long as bit 0 of N is a 1. The while loop - The statements inside a while statement, will continuously be executed if the while condition is true. Choose an unsigned integer less than as variable a, press run and follow the flow of the program and examine the output screen.

The loop continuously divides the variable a by 10 and outputs the result. A do-while loop performs the body first, and the test for completion second. It will execute the body at least once. ANDS R2, 0x20 ; bit 5 set? The do-while loop - The statements inside a do-while statement will always be executed once, and will continuously be executed if the while condition is true.

If the condition becomes false, the program will skip the loop and continue with the execution of the remaining statements. Choose an unsigned integers less than as variable a, press run and follow the flow of the program and examine the output screen. For loops can iterate up or down. To show the similarity between the while loop and for loop these two C functions are identical. For-loops are a convenient way to perform repetitive tasks.

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As an example, we write code that calls Process 10 times. Two possible solutions are illustrated in Figure 7. The solution on the left starts at 0 and counts up to 10, while the solution on the right starts at 10 and counts down to 0. The first field is the initialization task e. The next field specifies the conditions with which to continue execution e. If the condition evaluates to false we end the for loop, otherwise we continue another repetition before checking again. Similar to a while loop, the test occurs before each execution of the body.

Two flowcharts of a for - loop structure. The count-up implementation places the loop counter in the Register R4 , as shown in Program 7. As mentioned earlier, we assume the subroutine Process preserves the value in R4. Process ;. If we assume the body will execute at least once, we can execute a little faster, as shown in Program 7. Counting down is one instruction faster than counting up. The for loop - A for loop functionality is similar to a while loop, with automatic initialization and update.

It is usually used when the number of iterations is known.