Despite the best intentions, the competence, and the rigorous methods of designers and developers, software is often delivered and deployed with faults. To cope with imperfect software, researchers have proposed the concept of self-healing for software systems. The ambitious goal is to create software systems capable of detecting and responding “autonomically” to functional failures, or perhaps even preempting such failures, to maintain a correct functionality, possibly with acceptable degradation. We believe that self-healing can only be an expression of some form of redundancy, meaning that, to automatically fix a faulty behavior, the correct behavior must be already present somewhere, in some form, within the software system either explicitly or implicitly. One approach is to deliberately design and develop redundant systems, and in fact this kind of deliberate redundancy is the essential ingredient of many fault tolerance techniques. However, this type of redundancy is also generally expensive and does not always satisfy the time and cost constraints of many software projects. With this article we take a different approach. We observe that modern software systems naturally acquire another type of redundancy that is not introduced deliberately but rather arises intrinsically as a by-product of modern modular software design. We formulate this notion of intrinsic redundancy and we propose a technique to exploit it to achieve some level of self-healing. We first demonstrate that software systems are indeed intrinsically redundant. Then we develop a way to express and exploit this redundancy to tolerate faults with automatic workarounds. In essence, a workaround amounts to replacing some failing operations with alternative operations that are semantically equivalent in their intended effect, but that execute different code and ultimately avoid the failure. The technique we propose finds such workarounds automatically. We develop this technique in the context of Web applications. In particular, we implement this technique within a browser extension, which we then use in an evaluation with several known faults and failures of three popular Web libraries. The evaluation demonstrates that automatic workarounds are effective: out of the nearly 150 real faults we analyzed, 100 could be overcome with automatic workarounds, and half of these workarounds found automatically were not publicly known before.

We present a technique to make applications resilient to failures. This technique is intended to maintain a faulty application functional in the field while the developers work on permanent and radical fixes. We target field failures in applications built on reusable components. In particular, the technique exploits the intrinsic redundancy of those components by identifying workarounds consisting of alternative uses of the faulty components that avoid the failure. The technique is currently implemented for Java applications but makes little or no assumptions about the nature of the application, and works without interrupting the execution flow of the application and without restarting its components. We demonstrate and evaluate this technique on four mid-size applications and two popular libraries of reusable components affected by real and seeded faults. In these cases the technique is effective, maintaining the application fully functional with between 19% and 48% of the failure-causing faults, depending on the application. The experiments also show that the technique incurs an acceptable runtime overhead in all cases.

I present an approach to avoid functional failures at runtime in component-based application systems. The approach exploits the intrinsic redundancy of components to find workarounds as alternative sequences of operations to avoid a failure. A first Java prototype is presented, and an evaluation plan, as some preliminary results, are discussed.

Despite the best design practices and testing techniques, many faults exist and manifest themselves in deployed software. In this paper we propose a self-healing framework that aims to mask fault manifestations at runtime in Java applications by automatically applying workarounds. The framework integrates a checkpoint-recovery mechanism to restore a consistent state after the failure, and a mechanism to replace the Java code at runtime to apply the workaround.

Faults in Web APIs may escape the testing process, and therefore affect thousands of Web applications. As a consequence, users of these applications might suffer from related failures for a long time until proper fixes are released by the Web API developers. In this paper we present RAW, a tool that tries to find workarounds automatically and at runtime, thereby reducing the negative impact of faults in Web applications. Runtime and automatically deployed workarounds serve as a temporary relief for application users while proper fixes are developed and released.

We present a technique that finds and executes workarounds for faulty Web applications automatically and at runtime. Automatic workarounds exploit the inherent redundancy of Web applications, whereby a functionality of the application can be obtained through different sequences of invocations of Web APIs. In general, runtime workarounds are applied in response to a failure, and require that the application re-main in a consistent state before and after the execution of a workaround. Therefore, they are ideally suited for inter-active Web applications, since those allow the user to act as a failure detector with minimal effort, and also either use read-only state or manage their state through a trans-actional data store. In this paper we focus on faults found in the access libraries of widely used Web applications such as Google Maps. We start by classifying a number of re-ported faults of the Google Maps and YouTube APIs that have known workarounds. From those we derive a number of general and API-specific program-rewriting rules, which we then apply to other faults for which no workaround is known. Our experiments show that workarounds can be readily de-ployed within Web applications, through a simple client-side plug-in, and that program-rewriting rules derived from ele-mentary properties of a common library can be effective in finding valid and previously unknown workarounds.