Rehearsal: A Configuration Verification Tool for Puppet

Large-scale data centers and cloud computing have turned system configuration into a challenging problem. Several widely-publicized outages have been blamed not on software bugs, but on configuration bugs. To cope, thousands of organizations use system configuration languages to manage their computing infrastructure. Of these, Puppet is the most widely used with thousands of paying customers and many more open-source users. The heart of Puppet is a domain-specific language that describes the state of a system. Puppet already performs some basic static checks, but they only prevent a narrow range of errors. Furthermore, testing is ineffective because many errors are only triggered under specific machine states that are difficult to predict and reproduce. With several examples, we show that a key problem with Puppet is that configurations can be non-deterministic. This paper presents Rehearsal, a verification tool for Puppet configurations. Rehearsal implements a sound, complete, and scalable determinacy analysis for Puppet. To develop it, we (1) present a formal semantics for Puppet, (2) use several analyses to shrink our models to a tractable size, and (3) frame determinism-checking as decidable formulas for an SMT solver. Rehearsal then leverages the determinacy analysis to check other important properties, such as idempotency. Finally, we apply Rehearsal to several real-world Puppet configurations.Comment: In proceedings of ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI) 201

Managing Real-World System Configurations with Constraints

Managing large computing infrastructures in a reliable and efficient way requires system configuration tools which accept higher-level specifications. This paper describes an interface between the established configuration tool LCFG, and the experimental configuration tool PoDIM. The com-bined system is used to generate explicit real-world con-figurations from high-level, constraint-based specifications. The concept is validated using live data from a large pro-duction installation. This demonstrates that a loosely-coupled, multi-layer approach can be used to construct con-figuration tools which translate high-level requirements into deployable production configurations.

Hypothyroidism and the risk of lower extremity arterial disease

Background: Although an independent association between hypothyroidism and coronary artery disease has been demonstrated, few studies have examined the association between hypo-thyroidism and peripheral arterial disease. In the current study, we test the hypothesis that there is an independent association between hypothyroidism and lower extremity arterial disease. Methods: We retrospectively compared the prevalence of hypothyroidism in patients who had infra-inguinal arterial bypass surgery over a 6-year period with that of a control group of surgical patients who had pure cardiac valve surgery during the same time period. Both unadjusted and adjusted odds ratios were calculated to estimate the association between hypothyroidism and lower extremity arterial disease. Results: A total of 614 cases and 529 control subjects had surgery during the study period. When comparing all subjects, there was no association between hypothyroidism and lower extremity arterial disease (unadjusted odds ratio 0.88; 95% confidence intervals [CI]: 0.61-1.28). However, gender was found to be a significant effect modifier (P \u3c 0.001), and gender-stratified analyses were subsequently performed. In men, there was a positive independent association between hypothyroidism and lower extremity arterial disease (adjusted odds ratio 2.65; 95% CI: 1.19-5.89), whereas in women there was a negative independent association (adjusted odds ratio 0.22; 95% CI: 0.11-0.46). Conclusions: Gender is a significant effect modifier for the association between hypothyroidism and lower extremity arterial disease. The association is positive in men and negative in women. Future prospective studies that evaluate hypothyroidism as a risk factor for peripheral arterial disease should consider gender stratification in order to corroborate this finding. © 2010 Mazzeffi et al, publisher and licensee Dove Medical Press Ltd

Case Reports1. A Late Presentation of Loeys-Dietz Syndrome: Beware of TGFβ Receptor Mutations in Benign Joint Hypermobility

Background: Thoracic aortic aneurysms (TAA) and dissections are not uncommon causes of sudden death in young adults. Loeys-Dietz syndrome (LDS) is a rare, recently described, autosomal dominant, connective tissue disease characterized by aggressive arterial aneurysms, resulting from mutations in the transforming growth factor beta (TGFβ) receptor genes TGFBR1 and TGFBR2. Mean age at death is 26.1 years, most often due to aortic dissection. We report an unusually late presentation of LDS, diagnosed following elective surgery in a female with a long history of joint hypermobility. Methods: A 51-year-old Caucasian lady complained of chest pain and headache following a dural leak from spinal anaesthesia for an elective ankle arthroscopy. CT scan and echocardiography demonstrated a dilated aortic root and significant aortic regurgitation. MRA demonstrated aortic tortuosity, an infrarenal aortic aneurysm and aneurysms in the left renal and right internal mammary arteries. She underwent aortic root repair and aortic valve replacement. She had a background of long-standing joint pains secondary to hypermobility, easy bruising, unusual fracture susceptibility and mild bronchiectasis. She had one healthy child age 32, after which she suffered a uterine prolapse. Examination revealed mild Marfanoid features. Uvula, skin and ophthalmological examination was normal. Results: Fibrillin-1 testing for Marfan syndrome (MFS) was negative. Detection of a c.1270G > C (p.Gly424Arg) TGFBR2 mutation confirmed the diagnosis of LDS. Losartan was started for vascular protection. Conclusions: LDS is a severe inherited vasculopathy that usually presents in childhood. It is characterized by aortic root dilatation and ascending aneurysms. There is a higher risk of aortic dissection compared with MFS. Clinical features overlap with MFS and Ehlers Danlos syndrome Type IV, but differentiating dysmorphogenic features include ocular hypertelorism, bifid uvula and cleft palate. Echocardiography and MRA or CT scanning from head to pelvis is recommended to establish the extent of vascular involvement. Management involves early surgical intervention, including early valve-sparing aortic root replacement, genetic counselling and close monitoring in pregnancy. Despite being caused by loss of function mutations in either TGFβ receptor, paradoxical activation of TGFβ signalling is seen, suggesting that TGFβ antagonism may confer disease modifying effects similar to those observed in MFS. TGFβ antagonism can be achieved with angiotensin antagonists, such as Losartan, which is able to delay aortic aneurysm development in preclinical models and in patients with MFS. Our case emphasizes the importance of timely recognition of vasculopathy syndromes in patients with hypermobility and the need for early surgical intervention. It also highlights their heterogeneity and the potential for late presentation. Disclosures: The authors have declared no conflicts of interes

Survey of Configuration Management Tools

Over the last years, there has been an enormous boost in the number of solutions available for automating system configuration tasks. However, there is no generally accepted taxonomy framework that serves as a basis for evaluating configuration management solutions. In this report, we present such a taxonomy. We also appl

High-level system configuration

The high rate of requirement changes make system administration a complex task. This complexity is further influenced by the increasing scale, unpredictable behaviour of software and diversity in terms of hardware and software. In order to deal with this complexity, system configuration tools have been proposed. The processes that many system configuration tools advocate are kept close to manual system administration. We feel that this approach has failed to address the complexity of system administration in the real world. In this paper, we advocate a higher-level language for system configuration, prototyped in PoDIM. We introduce the use of constraints, dependency modeling and platform independence in the context of system configuration. We believe that high-level languages are needed to reduce system administration complexity. PoDIM is one step in that direction.status: publishe