The basic idea behind DevOps
is that your development strategy and operations strategy should reflect one another, that you should strive to optimize the whole IT process. This implies that development teams should work closely with your operations staff to deliver new releases smoothly into production and that your operations staff should work closely with development teams to streamline critical production issues.
DevOps has its source in agile software development, and it is an explicit aspect of the Disciplined Agile Delivery (DAD)
process framework. As a result there is a collection of agile development strategies which enable effective DevOps throughout the agile delivery lifecycle. These strategies include:
- Initial requirements envisioning. Disciplined agile teams invest time at the beginning of the project to identify the high-level scope in a light-weight, collaborative manner. This includes common operations requirements such as the need to backup and restore data sources, to instrument the solution so that it can be monitored in real time by operations staff, or to architect the solution in a modular manner to enable easier deployment.
- Initial architecture envisioning. Disciplined agile teams will also identify a viable architectural strategy which reflects the requirements of their stakeholders and your organization’s overall architectural strategy (hence the need to work closely with your enterprise architects and operations staff). One goal is to ensure that the team is building (or buying) a solution which will work well with the existing operational infrastructure and to begin negotiating any infrastructural changes (such as deploying new technologies) early in the project. Another goal is to ensure that operations-oriented requirements are addressed by the architecture from the very start.
- Initial release planning. As part of release planning the disciplined agile team works closely with their operations group to identify potential release windows to aim for, any release blackout periods to avoid, and the need for operations-oriented milestone reviews later in the lifecycle (if appropriate).
- Active stakeholder participation. Disciplined agile teams work closely with their stakeholders, including both operations and support staff, all the way through the lifecycle to ensure that their evolving needs are understood.
- Continuous integration (CI). This is a common technical agile practice where the solution is built/compiled, regression tested, and maybe even run through code analysis tools. CI promotes greater quality which in turn enables easier releases into production.
- Parallel independent testing. For enterprise-class development or at scale, particularly when the domain or technology is very complex or in regulatory environments, disciplined agile team will find they need to support their whole team testing efforts with an independent test team running in parallel to the development team. These testing issues often include validation of non-functional requirements – such as security, performance, and availability concerns – and around production system integration. All of these issues are of clear importance for operations departments.
- Continuous deployment. With this practice you automate the promotion of your working solution between environments. By automating as much of the deployment effort as possible, and by running it often, the development team increases the chance of a successful deployment and thereby reduces the risk to the operations environment. Note that deployment into production is generally not automatic, as this is an important decision to be made by your operations/release manager(s).
- Continuous documentation. With this practice supporting documentation, including operations and support documentation, is evolved throughout the lifecycle in concert with the development of new functionality.
- Production release planning. This is the subset of your release planning efforts which focuses on the activities required to deploy into production.
- Production readiness reviews. There should be at least one review, performed by the person(s) responsible for your operations environment, before the solution is deployed into production. The more critical the system, the more product readiness reviews may be required.
- End-of-lifecycle testing. Minimally you will need to run your full automated regression test suite against your baselined code once construction ends. There may also be manual acceptance reviews or testing to be performed, and any appropriate fixing and retesting required to ensure that the solution is truly ready for production.
There’s more to it though than simply adopting some good practices. Your process must also embrace several supporting philosophies. The Disciplined Agile Delivery (DAD)
process framework not only adopts the practices listed above, and more, but it also promotes several philosophies which enable DevOps:
- Delivery teams should be enterprise aware, that they should work with people such as operations staff and enterprise architects to understand and work towards a common operational infrastructure for your organization.
- Operations and support people should be recognized as key stakeholders of the solution being worked on.
- The delivery team should focus on solutions over software. Software is clearly important, but we will often provide new or upgraded hardware, supporting documentation (including operations and support procedures), change the business/operational processes that stakeholders follow, and even help change the organizational structure in which our stakeholders work.
- Your process should include an explicit governance strategy. Effective governance strategies motivate and enable development teams to leverage and enhance the existing infrastructure, follow existing organizational conventions, and work closely with enterprise teams – all of which help to streamline operations and support of the delivered solutions.
For more detail about this topic, I think that you will find the article I wrote for the December 2011 issue of Cutter IT Journal entitled “Disciplined Agile Delivery and Collaborative DevOps
” to be of value.
A recurring discussion that I have with experienced agile developers is what it means to take a disciplined agile approach. The conversation usually starts off by some saying "but it already requires discipline to do agile", something that I fully agree with, followed by "therefore 'disciplined agile' is merely a marketing term", something which I don't agree with. The challenge with the "standard" agile discipline is that it is often focused on construction activities within a single project team, clearly important but also clearly not the full picture. There's more to an agile project than construction, and there's more to most IT departments than a single development project. In short, there are many opportunities for IT professionals to up their discipline, and thereby up their effectiveness, opportunities which we make explicit in the Disciplined Agile Delivery (DAD) framework.
Let's explore the many aspects to taking a disciplined agile approach:
You adopt "standard" agile discipline
. Aspects of agile which require discipline
include adopting practices such as test-driven development (TDD), active stakeholder participation, working collaboratively, shortening the feedback cycle
, and many more. These strategies are a great start to becoming disciplined IT professionals.
You take a goal-driven approach
. When we first started working on the DAD framework I didn't want to create yet another prescriptive framework, particularly given Rational's track record with the Rational Unified Process (RUP) framework. Rational has been pilloried for years for the prescriptive nature of RUP, which is unfortunate because there are a lot of great ideas in RUP that agile teams can benefit from, some of which we adopted in DAD and many of which are being actively reinvented with the agile community even as you read this. Furthermore, there are many prescriptive elements of the Scrum method that can get teams in trouble. For example, Scrum prescribes that you hold a daily stand up meeting, often called a Scrum meeting, where everyone should answer three questions. That's a great approach for teams new to agile, but it proves problematic in many situations due to it's prescriptive nature. Do you really need to do this once a day? I've been on teams where we held coordination meetings twice a day and others only once a week. Do you really need to stand up? I've been on geographically distrubited agile teams where many of us were sitting down during coordination calls. Do you really need to answer three questions, two of which are clearly focused on status regardless of claims otherwise? I've been on lean teams where we met around our Kanban board and focused on potential blockers. The answers to these questions depends on the context of the situation you find yourself in. The challenge, at least from the point of view of a process framework, is how do you avoid falling into the trap of being overly prescriptive. The strategy we adopted in DAD is to take a goal-driven approach. The observation is that regardless of the situation you find yourself in there are common goals your team will need to fulfill. For example, at the beginning of a project common goals include developing an initial plan, initially exploring the scope, initially identifying a technical strategy, and securing initial funding (amongst others). Throughout construction you should coordinate your activities, improve the quality of your ecosystem, and produce a potentially consumable solution on a regular basis (more on this below). So, instead of prescribing a daily stand up meeting the DAD framework instead indicates you should coordinate your activities, and gives several options for doing so (one of which is a Scrum meeting). More importantly DAD describes the advantages and disadvantages of your options so that you can make the choice that's best suited for the situation your team finds itself in (see this blog posting
for a detailed example of the types of tables included in the DAD book to help you through such process tailoring decisions). In short, our experience is that it requires discipline to take a goal driven approach
to agile delivery over the prescriptive strategies in other agile processes.
You take a context-driven approach
. There are many tailoring factors, which I describe in the Software Development Context Framework (SDCF)
, which you need to consider when making process, tooling, and team structure decisions. For example, a large team will adopt a different collection of practices and tools than a small team. A geographically distributed team will adopt a different strategy than a team that is co-located. You get the idea. Other tailoring factors include compliance, team culture, organization culture, technical complexity, domain complexity, and project type. It requires discipline to recognize the context of the situation you find yourself in and then act accordingly.
You deliver potentially consumable solutions
. One of the observations that we made early in the development of the DAD framework was that disciplined agile teams produce potentially consumable solutions, not just potentially shippable software. Although delivery of high-quality, working software is important it is even more important that we deliver high-quality working solutions to our stakeholders. For example, not only are we writing software but we may also be updating the hardware on which it runs, writing supporting documentation, evolving the business processes around the usage of the system, and even evolving the organizational structure of the people working with the system. In other words, disciplined agilists focus on solutions over software
. Furthermore, "potentially shippable" isn't sufficient: not only should it be shippable but it should also be usable and should be something people want to use. In other words it should be consumable (a concept DAD adopted from IBM's Outside In Development
). Minimally IT professionals should have the skills and desire to produce good software, but what they really need are the skills and desire to provide good solutions. We need strong technical skills, but we also need strong "
such as user interface design and process design to name just two.
The incremental delivery of potentially consumable solutions on an incremental basis requires discipline
to do successfully. DAD teams focus on repeatable results not repeatable processes
You are enterprise aware
. Whether you like it or not, as you adopt agile you will constrained by the organizational ecosystem, and you will need to act accordingly. It takes discipline to work with enterprise professionals such as enterprise architects, data admistrators, portfolio managers, or IT governance people who may not be completely agile yet, and have the patience to help them. It takes discipline to work with your operations and support staff in a DevOps
manner throughout the lifecycle, particularly when they may not be motivated to do so. It requires discipline to accept and potentially enhance existing corporate development conventions (programming guidelines, data guidelines, UI guidelines, ...). It requires discipline to accept that your organization has an existing technology roadmap that you should be leveraging, building out, and in some cases improving as you go. In short, enterprise awareness requires a level of discipline
not typically seen on many agile teams.
You adopt a full delivery lifecycle
. Empirically it is very easy to observe that at the beginning of an agile project there are some activities that you need to perform to initiate the project. Similarly at the end of the project there are activities that you need to perform to release the solution into production or the marketplace. The DAD process framework addresses the effort required for the full delivery effort, including project initiation, construction, and deployment. Our experience is that it requires discipline on the part of IT professionals to include explicit phases
for Inception/Initation, Construction, and Transition/Deployment and more importantly to focus the appropriate amount of effort on each. One danger of explicit phases is that you run the risk of taking what's known as a Water-Scrum-Fall
approach, a term coined by Dave West the person who wrote the forward for the DAD book, where you take an overly heavy/traditional approach to inception and transition in combination with a lighter agile approach to construction. Water-Scrum-Fall occurs because many organizations haven't made a full transition to agile, often because they think it's only applicable to construction. Our experience is that you can be very agile in your approach to inception and transition, experience we've built into the DAD framework. Having said that it clearly requires discipline to keep inception activities short
and similarly it requires discipline to reduce the "transition phase" to an activity
You adopt a wider range of roles
. An interesting side effect of adopting a full delivery lifecycle is that you also need to adopt a more robust set of roles. For example, the Scrum method suggests three roles - Scrum Master, Product Owner, and Team Member - a reflection of the Scrum lifecycle's construction focus. DAD suggests three primary roles - Team Lead, Product Owner, Team Member, Architecture Owner
, and Stakeholder - as well as five secondary roles which may appear at scale.
You embrace agile governance
. Governance establishes chains of responsibility, authority and communication in support of the overall enterprise’s goals and strategy. It also establishes measurements, policies, standards and control mechanisms to enable people to carry out their roles and responsibilities effectively. You do this by balancing risk versus return on investment (ROI), setting in place effective processes and practices, defining the direction and goals for the department, and defining the roles that people play with and within the department. It requires discipline to adopt an agile approach to governance
, and that's something built right into the DAD framework.
Modified by ScottAmbler
On April 25, 2013 I gave a webcast for the Global Rational User Community entitled Disciplined Agile Delivery: Going beyond Scrum . During the webcast a large number of questions were asked but unfortunately I couldn’t get to all of them. So I’ve taken the opportunity to write up the answers in this blog posting.
Fequently asked questions. Many of the questions are addressed in the DAD FAQ.
DAD elevator pitch - I will be starting work in a couple of weeks for a company that has just started its Agile journey this year by implementing Scrum. What would Scott put in an elevator chat as to why they should be moving towards DAD. The Disciplined Agile Delivery (DAD) decision process framework is a people-first, learning-oriented hybrid agile approach to IT solution delivery. It has a risk-value delivery lifecycle, is goal-driven, is enterprise aware, and is scalable. There are clearly some interesting aspects to the DAD framework. DAD is a hybrid approach which extends Scrum with proven strategies from Agile Modeling (AM), Extreme Programming (XP), Unified Process (UP), Kanban, Lean Software Development, Outside In Development (OID) and several other methods. DAD is a non-proprietary, freely available framework. DAD extends the construction-focused lifecycle of Scrum to address the full, end-to-end delivery lifecycle from project initiation all the way to delivering the solution to its end users. It also supports lean and continuous delivery versions of the lifecycle: unlike other agile methods, DAD doesn’t prescribe a single lifecycle because it recognizes that one process size does not fit all. DAD includes advice about the technical practices such as those from Extreme Programming (XP) as well as the modeling, documentation, and governance strategies missing from both Scrum and XP. But, instead of the prescriptive approach seen in other agile methods, including Scrum, the DAD framework takes a goals-driven approach. In doing so DAD provides contextual advice regarding viable alternatives and their trade-offs, enabling you to tailor DAD to effectively address the situation in which you find yourself. By describing what works, what doesn’t work, and more importantly why, DAD helps you to increase your chance of adopting strategies that will work for you. The article Introduction to Disciplined Agile Delivery provides a more detailed description.
The book: Could you please repeat the name of the book that Scott is talking about? The book is Disciplined Agile Delivery: A Practitioner’s Guide to Agile Software Delivery in the Enterprise published by IBM Press, June 2012. The Disciplined Agile Delivery (DAD) website and the Disciplined Agile Consortium website are also good DAD resources.
The Surveys: Where is the data published about geographic distribution and effectiveness? All of my survey data, the original questions as asked, and my analysis can be downloaded free of charge from my IT Surveys page. If you ever see a request from me to fill out a survey, please take a few minutes and do so. I think you'll agree that my surveys page is in fact a very useful resource, so please contribute when you can.
Project success criteria: Where would a goal of defining success criteria fall? In the DAD book we describe how the success criteria for the project should be initially identified during Inception. Success criteria, like other things, could evolve throughout the project. You might find the IT Process Success Surveys to be of interest as several of them explored what success criteria projects actually have. Interestingly, its rarely “on time, on budget, to specification”.
Transitioning to DAD: How would you typically phase a DAD implementation, let's say in a project pilot where they haven't been exposed yet to Agile? Same question, any variance if the development team has already started Scrum? This is a fairly complex question to answer. The short story is that you need to invest some time to understand what your strengths and weaknesses are so that you can identify what you need to focus on. You will then likely need to pilot strategies/techniques which are new to your organization before rolling them out widely. You may also need to invest in training and coaching/mentoring depending on your needs. My company, Scott Ambler + Associates, offers these sorts of services and more for organizations interesting in adopting disciplined agile strategies.
Skills: I am aware that ideally developer should also be able to test but in reality theses are usually separate roles. Is it in line with your beliefs\suggestions? Many organizations that are new to agile still have roles that reflect their existing strategy. Non-agile approaches often have people in specific roles such as programmer, tester, designer, and so on. In DAD we promote a different set of agile roles that reflect agile thinking. The implication is that you’re going to have to help individuals transition over to the new way of thinking, something we cover in Chapter 4 of the DAD book. You might also find Mark Lines' blog, No role in DAD for an Analyst? to provide some insights into issues surrounding the transition from traditional to agile roles.
Teaming: What happens with the Product Owner and the Architecture Owner don’t Agree? See my blog What Happens When People Don’t Agree
Skillsets: Different people of the team have different skills, experience, and time horizons. We can't all be generalists, can we? There are several agile roles in DAD, each of which have different rights, responsibilities, and skillsets. So we’re not promoting the idea that everyone have the same skillset. However, we do promote the philosophy that people should strive to be T-skilled generalizing specialists so as to improve their productivity.
Teaming: What are your thoughts on team cohesion? Teams will gel over time. Being co-located helps. Having people who are dedicated 100% to the team helps. Building a team of people who want to be there helps. Self organization helps.
Tool support: Is there an RMC plug-in for DAD + Is there any software behind DAD... or some software that supports it... such as Jazz (RTC) for Agile/Scrum? Yes, IBM Rational does in fact have an RMC plug in for DAD. There is also a template for Microsoft TFS from RDA Corp, Software Development Expert’s Practices Advisor supports DAD comprehensively, and I’m currently working with MethodPark to do so too. Stay tuned to the Disciplined Agile Delivery website for information about tool support.
Governance: Regarding enterprise governance and enterprise IT, how do you start taking a culture that imposes common-process, common-tools, central (often outsourced) IT services, and heavyweight stage/gate across all organizations, and get that evolving toward a (still enterprise aware) lean/agile approach? This is a hard one. I’m often called into organizations to help with this very issue. The challenge is that you need to have a deep understanding of IT governance techniques as well as how to govern agile teams. Governance is something we discussed in detail in the DAD book as well as on the DAD site, see Adopting Agile Governance Requires Discipline.
Executable specifications: TDD was mentioned, can you comment on Behavior Driven Development (BDD) and any impact on this lifecycle? BDD is a slight nuance to acceptance test-driven development (ATDD). BDD/ATDD and TDD are both potential practices that you might choose to follow on a DAD team. I’ve written a fair bit about agile testing and quality strategies and about TDD in detail.
Architecture: When does the first version of architecture gets established and what would require to establish it? You typically start thinking about architecture early in a DAD project during Inception following a practice called architecture envisioning. I’ve also written a fair bit about agile architecture techniques and the potential misconceptions about agile architecture that you may find interesting.
Travel plans: Will you be coming to South Africa at some point? The good news is that Mark Lines, my co-author, will be in South Africa the week of May 20 in Joburg and the following week in Capetown. Contact us for details. I hope to be visiting SA later this year but exact dates haven’t been set yet. So, please stay tuned on Twitter at @scottwambler for further announcements.
Other travel plans: If you'd like me to speak at a local event, including corporate conferences or training events, please contact me.
Modified by ScottAmbler
A fair question to ask is why should your organization consider adopting the Disciplined Agile Delivery (DAD) process framework. I believe that there are several clear benefits to doing so:
DAD shows how agile techniques fit together. DAD is a hybrid that adopts strategies from a variety of sources, including Scrum, Extreme Programming (XP), Agile Modeling, Kanban, Outside In Development (OID) and many more. More importantly DAD's process-goal driven approach shows how this all fits together, providing advice for when (and when not) to use each technique and the advantages and disadvantages of doing so. In doing so DAD enables you to streamline your efforts to tailor agile to reflect the context of the situation you find yourself in. Furthermore, it provides this advice in the context of a full agile delivery lifecycle, explicitly showing how to initiate a project, construct a solution, and then deploy into production. Instead of starting with a small agile method such as Scrum and doing all the work to figure out how to tailor ideas from other methods to actually make it work, why not start with a framework that's already done all that work for you?
DAD isn't prescriptive. DAD is far less prescriptive than other agile methods. For example, where Scrum prescribes a single strategy for managing changing requirements, a strategy called a Product Backlog, DAD suggests several strategies and provides advice for choosing the right one. Where other agile methods define a single lifecycle, DAD instead describes several lifecycles (an agile Scrum-based one, a lean lifecycle, and a continuous delivery lifecycle to name just three) and once again describes how to choose the right one for your situation. Your agile team is in a unique situation, and as a result needs a flexible process framework that provides coherent, easy-to-follow tailoring advice. Isn't it better to adopt strategies that reflect the context that you actually face?
DAD explicitly addresses architecture. Even after a decade of agile software development it still seems that the topic of how agile teams address architecture is a mystery for many people. As a result DAD builds agile architecture strategies right in, starting with initial architecture envisioning, to proving the architecture with working code, to evolutionary design strategies during construction.
DAD explicitly addresses DevOps. DevOps is the art of combining development and operations approaches in such a way as to streamline your overall efforts. DAD "bakes in" DevOps through explicit support for common DevOps practices as well as its robust stakeholder definition which explicitly includes operations and support people.
DAD explicitly addresses governance. Although governance is often considered a dirty word within some agile circles, the reality is that software development teams can and should be governed. Sadly, many agile teams have traditional governance strategies inflicted upon them, strategies which invariably increase schedule, cost and risk on the project. But is doesn't have to be this way. It is possible, and very desirable to adopt agile goverance strategies, strategies which are built right into the DAD framework.
DAD explicitly addresses many other important development activities. Architecture, DevOps, and governance are just the tip of the iceberg. DAD also shows how critical activities such as analysis, design, testing, quality, technical writing, and many more are addressed in an agile and streamlined manner throughout the delivery lifecycle. As described earlier, this is done in a non-prescriptive and tailorable manner, thereby removing a lot of the mystery regarding how this agile stuff all fits together into a coherent whole.
DAD is solution focused, not software focused. Although the rhetoric around "potentially shippable software" resonates well with developers it observably and empirically misses the mark. DAD promotes the more robust idea of "potentially consumable solutions". Yes, shipping is nice but shipping something that people actually want to use/buy, something that is consumable, is much nicer. Yes, software is part of the equation but that software runs on hardware, we often also need to develop supporting documentation, we often evolve the business process, and even evolve the organization structure around the usage of the system. In other words, we're really producing solutions, not just software. Isn't it better to adopt rhetoric that actually reflects what we're doing in practice?
DAD promotes enterprise awareness over team awareness. One of the great benefits of an agile approach to software development is its focus on the team. This can also be a bit of a problem, because a team-focused strategy can result in suboptimal decisions for your overall organization. DAD promotes the idea that disciplined agilists should be enterprise aware, working towards common business and technical goals while leveraging and enhancing the existing infrastructure whenever possible.
DAD provides a foundation from which to scale. The starting point for scaling agile is to understand how agile strategies fit together from project initiation to delivery into production. If you don't know how to succeed with agile in a straightforward situation then it will prove very difficult to do so in an agility @ scale situation. DAD not only provides this tailorable foundation from which to scale agile it also takes a robust view of what it means to scale agile (hint: large or distributed teams are only a start).
DAD provides a basis for enterprise agile. As organizations move towards a true "enterprise agile" approach they often find that they need to adopt either DAD as a foundation or invest a fair bit of effort inventing something similar. They are also starting to adopt strategies from the SAFe framework, or reinventing such, as well as ideas from sources such as Enterprise Unified Process (EUP) (sadly, poorly named in hindsight), ITIL, and even CoBIT. More on this in a future blog posting.
In short, DAD provides a lot of proven advice culled from years of experience applying agile software techniques in enterprise-class environments. Instead of figuring all of this stuff out on your own, why not jump ahead and leverage the hard-won lessons learned from other organizations that have already dealt with the challenges that you're struggling with today?
The primary shortcoming of the DAD framework is it makes it very clear that software development, oops I mean solution delivery, is quite complex in practice. As IT practitioners we inherently know this, but it seems that we need to be reminded of this fact every so often. DAD doesn't provide a simplistic, feel-good strategy that you can learn in a few hours of training. Instead it defines a coherent, tailorable strategy that reflects the realities of enterprise IT.
There is a wealth of information at DAD posted at the Disciplined Agile Delivery (DAD) web site and great discussions occuring on the DAD LinkedIn discussion forum. For those of you interested in agile certification, the Disciplined Agile Consortium site will prove valuable too, in particular the list of upcoming DAD workshops provided by several IBM partners. And of course the book Disciplined Agile Delivery: A Practitioner's Guide to Agile Software Delivery in the Enterprise (IBM Press, 2012) written by Mark Lines and myself is a very good read.
Modified by ScottAmbler
Over the past few months I've had several people ask me whether it makes sense to offshore agile testing, and more importantly when it makes sense to do so. So I thought I would share my thoughts on the subject:
Focus on whole team testing. The basic strategy is that agile teams should strive to do as much, if not all, of the testing themselves. We call this whole team testing. For organizations new to agile this can be daunting because they may be organized in such a way that programmers write code and then hand it over to testers for validation and verification. The implication is that organizations will need to invest in their staff so that the programmers become more well rounded and pick up testing skills (we refer this as moving from being a specialist to a generalizing specialist).
Offshore entire development teams. A common strategy for organizing geographically distributed agile teams is to have whole teams at each location. For example, if your larger team is spread across three locations - Toronto, London, and Bangalore - then each team is responsible for implementing end to end functionality. With a component-based approach the Toronto team should be fully responsible for one or more subsystems, the London team responsible for one or more subsystems, and the Bangalore team responsible for one or more subsystems. With a feature-team approach the Toronto team would implement all of the functionality, end-to-end, for a feature regardless of which subsystems that functionality affects. Agile teams typically aren't organized by job function (e.g. analysis is done in London, design and coding in Toronto, testing in Bangalore) due to the overhead of handoffs between sites, the increased risk of miscommunication due to less effective ways of communicating information, and the increased complexity of managing the work.
Adopt independent testing at scale. You may choose, or be forced to have, an independent test team that focuses on some of the more complex forms of testing. The general idea is that this team works in parallel to other subteams and tests their working builds on a regular basis. Having said that, the vast majority of the testing effort should still be done in a whole team fashion. If your team is experiencing agile scaling factors such as domain complexity or technical complexity then you may find that it makes economic sense to have an independent test team focus on forms of testing that are difficult for the subteams to address, in particular pre-production system integration testing. If your team is in a regulatory domain where independent testing is required, then you're better off to "shift left" this effort with an independent test team to reduce both cost and risk.
Offshore independent testing carefully. I would offshore independent testing only to organizations that I have a very good, long-term relationship with that have proven that they can work in a disciplined agile manner. I would also want to ensure that they have actual experience with agile independent testing AND are staffing the team with people that have that experience. A clear sign that they don't understand what is required is if the independent testing team is asking for a detailed requirements specification, an indication that they're planning on doing confirmatory testing which is better suited for whole team testing. Furthermore, I would only do this if I don't have adequate staff to do so myself AND do not have time to build up my own independent test team.
I suspect that you're going to find yourself in serious trouble if:
You do not have successful experiences with agile delivery in simpler (e.g. non-offshoring) situations first. Walk before you try to run.
You think you can save money by having agile programming done in one location and agile testing in another (the coordination costs are going to be much larger than you think)
You're offshoring testing because you're new to agile (in this situation you don't have the experience to organize let alone govern the offshored activities)
You work with a service provider where you don't have a proven track record with them when it comes to agile development (a proven track record with traditional approaches is a good start but still very risky)
In short, it can make sense to offshore agile testing in a very narrow range of situations. Be very careful.