Troubleshooting in Windows Azure
Troubleshooting refers to the general task of locating and understanding unexpected application behavior and correcting it. When developing applications, developers test, run, and debug their applications before deploying them into a production environment. This fact is true whether the application runs on a desktop computer or a server in the cloud. However, a widely distributed, multi-instance application designed for scale-out can be hard to debug, requiring more than standard tools and approaches.
For this reason, cloud applications should be designed with troubleshooting in mind. How you design troubleshooting support into your application depends first on where your application runs, and second on which languages or runtimes your application is built with or uses.
If you are building an application that runs on a Windows Azure Virtual Machine, in many cases, you can approach troubleshooting design as well as debugging as you would on the operating system if it were running on your own servers.
Applications running on Windows Azure are widely distributed, multi-instance applications that can be hard to debug. These types of applications require more than standard tools and approaches to troubleshooting. This topic discusses some proven troubleshooting practices and contains links to more intensive information on the practices described.
Note: This topic assumes you are either designing your application or have successfully deployed your Windows Azure application and that something unexpected is now occurring. It does not discuss how to deploy an application on Windows Azure. For more information about developing and deploying your Windows Azure application, see https://www.windowsazure.com/en-us/develop/overview/.
This topic first describes some best practices that will help you design your application so that you can troubleshoot effectively when problems occur. (If you do not design your application to enable you to follow the code flow in advance, it can be very hard to locate problems when they do occur.) These best practices are valid for all types of applications running on Windows Azure, regardless of the application model or language used.
The following sections describe specific approaches for developing supportable Windows Azure applications regardless of the type of application: Web Sites, Cloud Services, or Virtual Machines.
Each section describes best practices at a high level, and contains pointers to resources that demonstrate best practices in detail or describe how to implement them.
In this Document
Best Practices for Troubleshooting in Windows Azure
This section describes best practices that apply to Windows Azure applications no matter which hosting model or language you use. It contains resources for more in-depth discussion of those practices.
To build the foundation for efficient troubleshooting in Windows Azure, concentrate your efforts in these three main areas:
- Handling Failures Gracefully - Each component service must be able to endure the failure of dependent services or infrastructure.
- Tracing, Logging and Monitoring - Each component service must have the proper debugging, tracing, event, and error logging.
- Debug errors where you can – Before promoting for production, but also at the component and network level when running.
Designing an application with these ideas in mind allows the application to provide you with the information necessary to track down unexpected behavior when it occurs.
Design to Handle Errors Gracefully
Applications should handle error conditions gracefully if they can. This is even more important given the distributed nature of Windows Azure. Effective troubleshooting begins with a good transient-failure handling design. Transient errors are one of the main areas in which cloud applications fail to behave as expected due to transient error conditions inherent to internet applications.
Transient errors are failures related to latencies and intermittent network connections inherent in shared resources on the internet. Some examples are:
- Shared computer resources such as Windows Azure Cloud Services and SQL Database (to give two examples) can be slightly less or more responsive from moment to moment.
- Responsiveness delays due to providing durability for services. For example, SQL Azure keeps multiple copies of databases consistent in order to provide durability, this has an impact on responsiveness.
- Delays caused by HTTP or other protocol connections ending prior to completing work. For example, HTTP requests may not reach an endpoint and return prior to their timeout period.
To help alleviate the impact of transient errors, Windows Azure applications should:
- Be loosely coupled so that components are not locally dependent upon services that fail more often than in on-premise environments.
- Make asynchronous calls whenever possible to keep processes from becoming dependent on immediate responses.
- Use a transient error handling approach that detects certain categories of failures and can implement retry behavior for those failures based on some configurable retry policy.
Calls to services should either build or use a transient error handling layer to detect common failure scenarios and retry the call based upon a configuration setting. For .NET developers, one recommended library is the Microsoft Enterprise Library 5.0 Integration Pack for Windows Azure. Microsoft Enterprise Library is a collection of reusable application blocks that address common cross-cutting concerns in enterprise software development. The Microsoft Enterprise Library Integration Pack for Windows Azure is an extension to Microsoft Enterprise Library 5.0 that can be used with Windows Azure. It includes the Autoscaling Application Block, Transient Fault Handling Application Block, blob configuration source, protected configuration provider, and learning materials. Another, simpler .NET library with fewer features is the Cloud Application Framework & Extensions (CloudFx). CloudFx offers a set of production quality components and building blocks intended to jump-start the implementation of feature-rich, reliable, and extensible Windows Azure-based solutions and services.
Perform Appropriate Tracing and Logging
Because the complexity of distributed, scale-out applications, traditional debuggers that work against one process are of mush less use when investigating issues that are occuring while your application is running. Therefore tracing and logging are of upmost importance. The execution of your app and its data is shared across many services, which are hosted on many different machines. In a large scale distributed application, it is difficult, if not impossible to determine which service instance to attach to and debug. Tracing and logging allow you to follow application execution and data flow giving you a better understanding of the state of your application.
Successful Windows Azure applications have a logging and tracing strategy designed in to the application from the beginning. This reduces the time and effort required to locate any issues and repair them quickly without having to call Microsoft for support.
Note: Writing traces and logging extensively has a performance impact; doing so intensively has a more profound one. Therefore the design of your application should include a configurable tracing and logging policy that can be adjusted at need. Ideally, the level of logging should be adjustable from the ServiceConfiguration.cscfg file so that it can be changed without having to redeploy.
Having volumes of logs does not guarantee speedy bug detection and repair; a large amount of data takes a long time to decipher, and collecting it impacts the performance of your application. Adjustable logging controls both the size and storage cost of log data.
In the MSDN Magazine article Take Control of Logging and Tracing in Windows Azure, Mike Kelly describes four types of diagnostic output to consider:
- Debug Output - Only in debug build, includes asserts
- Tracing - Tracks the flow of control during execution
- Event Logging - Major events in program execution
- Error Logging - Exceptional or dangerous situation
Other languages, application platforms, and operating systems may have different terminology for tracing and logging. If you are using one of these development platforms on Windows Azure, use the equivalent strategy and tools for the language or the platform you are using.
Mixed mode applications are applications executing in a combination of Windows Azure Virtual Machines, Web Sites, and Cloud Services. When building applications of this type, tracing and logging become even more important because they are more widely distributed. To troubleshoot these mixed-mode applications the overall data and execution flow must be followed in order to identify any problems. The mechanics of tracing and logging a mixed mode application depends upon the hosting model of the component.
Monitor Your Application
Tracing and logging fit in to the bigger area of monitoring. Monitoring allows you to:
- Discover Windows Azure applications
- Determine status of each role instance
- Collect and monitor performance information including latency and throughput
- Collect and monitor events
- Collect and monitor trace messages
- Monitor resource usage
- Monitor quality of service metrics
- Perform capacity planning
- Perform traffic analysis (users, views, peak times)
- Estimate billing
- Perform auditing
Monitoring is accomplished with a tool or set of tools. Which tool you use depends on the platform and/or languages your application uses and on your monitoring goals and requirements.
Microsoft System Center Monitoring Pack for Windows Azure Applications
This Monitoring Pack allows you to use Microsoft System Center Operations Manager to monitor the availability and performance of Windows Azure Applications.
Using Microsoft System Center Operations Manager 2007 is the best way to monitor the health of your Windows Azure application.
Windows Azure Platform Management Tool
Another tool is the Windows Azure Platform Management Tool (MMC), which enables you to manage your Windows Azure hosted services and storage accounts. This tool is provided as a sample with complete source code so you can see how to perform various management and configuration tasks using the Windows Azure Management and Diagnostics APIs.
Cerebrata provides a number of tools that allow you to monitor and manage your Windows Azure applications. These include Azure Diagnostics Manager, Cloud Storage Studio, and Azure Management Cmdlets.
Azure Diagnostics Manager 2 is a Windows (WPF) based client for managing Windows Azure Diagnostics. It lets you view, download, and manage the diagnostics data collected by applications running in Windows Azure. See http://www.cerebrata.com for more information on these products.
Cloud Storage Studio 2 is a Windows (WPF) based client for managing Windows Azure Storage.
Azure Management Cmdlets is a set of Windows PowerShell cmdlets for managing Windows Azure Storage, Hosted Services, SQL Database instances, and Diagnostics. It also provides cmdlets to back up and restore storage accounts.
Network Monitoring: AlertBot, Gomez, Keynote, Pingdom
Compuware's Gomez Application Performance Management, Keynote, Pingdom, and AlertBot are solutions for monitoring your Windows Azure application remotely. They allow you to monitor the availability of your application and optimize performance. Some services, such as Pingdom, enable notification by email, SMS, or a desktop application when an error is detected. This type of monitoring simulates what an end user does to successfully monitor an application.
Apica provides tools that monitors your Windows Azure web application "from outside." For more information, see http://www.apicasystem.com/integration-partners/.
Microsoft purchased AVIcode and it is now part of Microsoft System Center. AVIcode delivers .NET application performance monitoring capabilities with a comprehensive suite of application monitoring capabilities.
You can profile your Windows Azure application when it runs in Windows Azure to determine any performance issues. When you publish your Windows Azure application from Visual Studio, you can choose to profile the application and select the profiling settings that you require.
Windows Azure VM Assistant
The VM Assitant tool is a CodePlex project that collects all the relevant troubleshooting data in one place when you Remote Desktop into an virtual machine instance. The VM Health button gives the current status of the instance.
Debugging Errors Where You Can
Before deploying an app to Windows Azure, it is a best practice to debug your application locally. The Windows Azure SDK contains emulators that mimic the Windows Azure cloud environment, allowing you to run your app and do rudimentary tests without having to deploying your application. The debugging tools you use vary depending upon the programming language and the development tools you are using.
After an application has been deployed, you can debug in the cloud using a debugger like Visual Studio. The requires creating a debug build and deploying it. In order to do this,you must connect to a specific role instance. If you have a complex application with multiple roles and role instances, it can be very difficult to determine to which role instance to connect. Visual Studio 2010 Ultimate supports IntelliTrace, which allows .NET roles to track debug information. When a problem occurs you can download this information and load it into Visual Studio. You can look at each role instance's IntelliTrace log to determine where the problem occured. While there are some drawbacks to debugging in the cloud, there are some circumstancesin which it is required. Not all Windows Azure Services have an emulator (for example Service Bus) and not all supported development tools (for example Mac and Linux) come with emulators.
*Once you have debugged your application locally you will most likely have to rely on the instrumentation built into your application to determine where problems are occurring. *
For debugging Node.JS applications, you can use the Node-Inspector tool which is available on GitHub. Node-Inspector can be run locally on your development machine using the Windows Azure storage emulator. For more information see Jim Wang’s blog: Debugging Node in the Windows Azure Emulator.
If you are debugging your application on Azure, install the full version of IISNode from GitHub on your web role, worker role, or VM instance. As discussed earlier, this is not a recommended way to debug your application when it is in production and scaled to multiple instances because you may not know to which role instance or VM to debug.
To use Node-Inspector on a web role, install the package in the web role and use the Node-Inspector tool as you normally would. For more information about debugging with Node-Inspector, see Debugging with Node-Inspector.
Microsoft Visual Studio 2010 Ultimate contains IntelliTrace, which can be enabled to debug applications before deployment into production. IntelliTrace supports ASP.NET, and WCF applications. Intellitrace is not supported when it is enabled in a production service, but can be used to get exceptions for an application after deployment to Windows Azure. Jim Nakashima's blog post describes how to use IntelliTrace to debug Windows Azure Cloud Services.
Fiddler is a Web Debugging Proxy that logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler is especially helpful for troubleshooting Windows Azure Storage.
To use Fiddler against the local development fabric, use ipv4.fiddler instead of 127.0.0.1:
- Launch Fiddler.
- Launch your service in the development fabric.
- Browse to http://ipv4.fiddler:/. Fiddler should trace the request.
To use Fiddler against the local development storage, modify the service configuration file to point to Fiddler:
Open the ServiceConfiguration.cscfg file and change the connection string to:
- Launch Fiddler.
- Launch your service. Fiddler should trace any storage requests.
Troubleshooting and the Windows Azure Hosting Models
This section discusses best practices for debugging applications using the different Windows Azure hosting models.
Windows Azure Web Sites
When designing a supportable Windows Azure web site, follow the recommendations made earlier in this document when possible. This includes checking for and handling errors, applying transient fault retry logic, tracing, and logging. Troubleshooting Windows Azure web sites is accomplished by configuring web sites to display application errors, configuring diagnostics for a web site, collecting diagnostic data and then analyzing the collected data to identify and resolve problems.
Windows Azure web sites enable configuration of the following diagnostic options:
- Web Server Logging
- Detailed Error Messages
- Failed Request Tracing
For more information on these topics see: Troubleshooting a Windows Azure web site.
When web server logs for Windows Azure web sites are enabled, the web site will record all HTTP transactions into a log file using the W3C extended log file format. You can then use Log Parser to query the log file. Some example log parser queries are available on Log Parser Plus and TechNet Log Parser Examples. If you want to generate the CHART output type on a computer that is running Office 2007/2010, install Office 2003 Web Components following the instructions on Log Parser Plus.
Windows Azure web sites uses the same failed request tracing functionality that has been available with IIS 7.0 and later. It is not, however, configurable like IIS failed request tracing. When you enable failed request tracing for Windows Azure web sites, all failed requests are captured.
Windows Azure Cloud Services
Because of the distributed nature of Windows Azure Cloud Services, it’s important to defend your application by making calls asynchronously and handling retries for transient failures, as described previously.
The debugging technique used for Windows Azure Cloud Services depends on the type of problem you are experiencing. Problems involving a specific role or role instance, for example a role failing to start or cycling, are best investigated using Remote Desktop. In these cases you will know which role or role instance is problematic and you can connect to the affected role. When a problem occurs and you are not sure what role instance is causing the problem, tracing and logging is a better method for troubleshooting. Windows Azure Diagnostics provides a mechanism to collect and manage trace and log information.
Some new debugging features have been added to the Windows Azure SDK 1.7 including making it easier to find stack traces when exceptions occur and improvements in Remote Desktop connectivity. Stack traces are now included in the Windows Event Log, making it easier to see exactly what went wrong. In addition Remote Desktop connectivity has been improved. If your role is cycling or aborted you will be able to use Remote Desktop to connect to the problematic role and investigate the problem.
The windows Azure Portal provides access to monitoring data that helps IT professionals and developers anticpate and diagnose problems in Windows Azure Cloud Services. By default values such as “CPU Percentage”, “Data In”, “Data Out”, “Disk Read Throughput” and “Disk Write Throughput” are collected by the host VM. There is no configuration needed to enable these metrics for role instances and there is no cost impact to customers. Additional performance information can also be collected. To collect verbose diagnostic information you must have a valid diagnostics connection string as this information will be stored in Windows Azure Storage and will therefore incurr additional storage costs. When user enables verbose monitoring, the portal will remotely configure role instances to collect the default set of performance counters.
Windows Azure Diagnostics
The original Windows Azure SDK 1.0 included functionality to collect diagnostics data and store them in Windows Azure storage collectively known as Windows Azure Diagnostics. This software, built upon the Event Tracing for Windows (ETW) framework, fulfills two design requirements introduced by Windows Azure scale-out architecture:
- Save diagnostic data that would be lost during a reimaging of the instance.
- Provide a central repository for diagnostics from multiple instances.
After configuring Diagnostics in the role, Diagnostics collects diagnostic data from all the instances of that particular role. The diagnostic data can be used for debugging and troubleshooting, measuring performance, monitoring resource usage, traffic analysis and capacity planning, and auditing. Transfers to Windows Azure storage account for persistence can either be scheduled or on-demand.
Windows Azure Diagnostics changes the server paradigm in four important ways:
- Diagnostics must be enabled at application creation time.
- Specific tools/steps are needed to visualize diagnostic results.
- Crashes will cause the loss of diagnostic data unless it is written to durable storage (Windows Azure Storage as opposed to being on each instance).
- Diagnostic storage incurs a monthly cost when stored in Windows Azure storage.
Cost is of particular importance because one of the key benefits of Windows Azure is cost reduction. The only way to eliminate the cost of using Diagnostics today is to leave the data on the virtual machine. This may work in a small deployment, but is impractical where there are many instances. Here are a few ways to minimize the financial impact:
- Make sure that the storage account is in the same data center as your application. If for some reason they are not in the same data center, choose the interval of scheduled transfers wisely. Shorter transfer times will increase data relevance, but that trade off may not be great enough to justify the additional bandwidth and processing overhead.
- Periodically copy and clear the diagnostic data from Windows Azure Storage. The diagnostic data will transit through Windows Azure storage, but not reside there unnecessarily. There are a number of tools to do this: System Center Monitoring Pack for Windows Azure, Cerebrata's Azure Diagnostics Manager, and Windows Azure PowerShell cmdlets.
- Choose only the diagnostic data that you will need to troubleshoot and monitor your application. Capturing too much data may make it harder to troubleshoot in addition to costing significantly more.
- Control the collection and extent of diagnostic data by implementing an on-demand switch in your application.
- Utilize the logging level (Verbose, Info, Warning, Error) so that all information is available, then utilize the post-deploy Diagnostics config to selectively gather data.
Windows Azure PowerShell Cmdlets
You can remotely manager diagnostics by using Windows Azure PowerShell Cmdlets. The cmdlets are based on the Windows Azure Management and Diagnostics APIs and the full source code is available through the CodePlex project so you can better understand the underlying APIs.
The Windows Azure PowerShell Cmdlets are designed to be usable tools for browsing, configuring, and managing several Windows Azure services. However, they are also provided in source code form to enable you to better understand how to use the services. Some of the key features demonstrated include:
- Windows Azure Service Management API
- Windows Azure SDK
- Windows Azure Storage Analytics
- Windows Azure Diagnostics
- SQL Database REST API
- Windows Azure Traffic Manager REST API
- Windows PowerShell
Documentation for the cmdlets can be found here: http://wappowershell.codeplex.com/documentation. Michael Washam's blog gives some good example scripts.
Windows Azure Virtual Machines
Troubleshooting applications running on Windows Azure Virtual Machines typically involve the same troubleshooting techniques that you would use with the operating systems and platforms in use. For example:
Troubleshooting Windows Azure Services
Many of the Windows Azure services such as Windows Azure SQL Database, Windows Azure Active Directory, and Windows Azure storage have troubleshooting advice that is specific to their use, regardless whether the application is executing on Windows Azure, what programming language or libraries it was built with, or executing on a non-Microsoft operating system. The following information provides best practices specific to some of these services.
There are many supported libraries that implement best practices for asynchronous calls, traces, and event logging as outlined in the design portion of this document.
Windows Azure Storage Troubleshooting
The following links discuss either designs or practices to mitigate problems requiring troubleshooting or locations in which you should add tracing or logging work.
Azure Storage Explorers
There are a number of ways to explore Windows Azure storage. The Windows Azure Storage team came up with a list of storage explorers. Any of these will allow you to see Diagnostics files and Windows Azure Storage Analytics files. Cloudberry Lab's Explorer for Azure Blob Storage provides a user interface to enable Storage Analytics directly in the application by clicking Storage Settings.
Windows Azure Service Bus Troubleshooting
This section provides high-level guidance about how to develop an application that uses the Windows Azure Service Bus in a robust and maintainable way that will minimize common issues. It also provides details about how to identify and address common Service Bus errors.
The Service Bus is an internet-scale enterprise service bus that supports relayed and brokered messaging capabilities. The Service Bus implements quotas and thresholds at a system level for both types of messaging. If your application exceeds these quotas, it will be throttled or your requests or messages will be rejected. For full details about Service Bus quotas and the behavior you will see when they are exceeded, see Windows Azure Service Bus Quotas. Some quotas are user defined, for example the size of a queue or topic, which is defined when the entity is created.
To get a view into the data in your Service Bus messaging entity and how it is being processed, you can use Service Bus Explorer or the Server Explorer in the Windows Azure Tools for Visual Studio version 1.7 to create, delete, and test queues, topics, subscriptions, and rules. This is an excellent way to troubleshoot an application that is running but not processing data the way you expect. These tools include functionality that enables you to test queues, topics, and relay entities, trace the operations performed by individual sender and receiver tasks, monitor progress and performance of an ongoing test run, and generate detailed logs of the results, including any error messages.
Service Bus Relay
The Service Bus “relay” service runs in the cloud and supports a variety of different transport protocols and Web services standards, including SOAP, WS-*, and REST. You can use the Service Bus relay as a delegate to listen for incoming sessions and requests sent to a WCF service. In the relayed messaging pattern, an on-premises or cloud-based service connects to the relay service through an outbound port and creates a bi-directional socket for communication tied to a particular rendezvous address. The client does not have to know where the service resides, and the on-premises service does not need any inbound ports open on the firewall. However, depending on your network configuration, you may encounter problems when connecting to the Service Bus relay from behind a firewall or through a proxy server. Hosting Behind a Firewall with the Service Bus describes how to troubleshoot and resolve such connection issues.
Service Bus Queues and Topics
Service Bus queues and topics provide brokered messaging functionality—messages are pushed to the Service Bus queue or topic where they are reliably retained until the receiver is ready to consume them. Message senders and receivers do not have to be online at the same time; the messaging infrastructure reliably stores messages until the consuming party is ready to receive them. The messaging API can encounter a variety of errors that might impact your application. These can be broadly grouped into the following categories:
- User error—for example, a code indicating an argument was invalid. Recommended action: Try to fix the code before proceeding.
- Setup/configuration error—for example, a queue or topic associated with the action does not exist or has been deleted. Recommended action: Review your configuration and change it if necessary.
- Transient error—for example, a response indicating that the service was not able to process the request at the current time. Recommended action: Retry the operation or notify users. For more information, see Handling Transient Communication Errors.
- Other errors—for example, timeout errors or errors indicating that a message lock was lost. Recommended action: You generally do not handle these exceptions to perform cleanups or aborts. They might be used for tracing.
Messaging Exceptions provides an overview of exceptions that users of the Service Bus client libraries for .NET might encounter, along with recommendations about how to handle each type of exception. Because the client libraries for .NET align closely to the structure of the Service Bus libraries for other languages, this guidance may be useful even if you are not programming in a .NET language. In some cases, for example with transient errors, you can retry the action. You can follow the transient error handling guidelines outlined earlier in this article to efficiently handle transient errors. In addition, for more details, best practices, and sample code that demonstrates how to handle transient Service Bus errors in a .NET application, see the Handling Transient Communication Errors section in the Windows Azure Developer Guidance article Best Practices for Leveraging Windows Azure Service Bus Brokered Messaging API.
Another area to focus on when developing an application that uses brokered messaging is to ensure you implement reliable message receiving logic that can accurately and efficiently handle anomalies in messages. The “Implementing Reliable Message Receive Loops” section of the Best Practices for Leveraging Windows Azure Service Bus Brokered Messaging API article describes a number of techniques for using the PeekLock receive mode, which is the mode that supports multiple message deliveries if the message isn’t delivered successfully on the first try. The article recommends best practices that will help ensure your application does not process duplicate messages. It also helps avoid problems that can occur due to lock timeouts, and improve overall performance in PeekLock mode by ensuring that you process messages promptly. The article also provides sample code that uses the Service Bus client libraries for .NET.
Additional Troubleshooting Resources
For additional details about common Service Bus errors and ways to investigate and address them, see Troubleshooting the Service Bus.
Windows Azure Active Directory Access Control Service (ACS)
Windows Azure SQL Database Troubleshooting
When interacting with a Windows Azure SQL database extra care must be taken to deal with the distributed nature of Windows Azure SQL Database applications. This section discusses several areas that warrant attention. This is by no means an exhaustive list. The key to writing supportable Windows Azure SQL Database code is to examine the return codes and make sure that you have solid retry code to handle failures.
Your application must handle login failures gracefully. SQL Database instances require the use of SQL Authentication. If you cannot successfully log in, either your credentials are not valid or the database you requested is not available.
Your application must handle the service being inaccessible. If the server is already provisioned and the Windows Azure SQL Database service is available (you can check this using the Azure Health Status page), the likely cause is configuration issues in your on-site installation. For instance, you may be unable to resolve the name (which can be tested with tools such as tracert), you may have a firewall blocking port 1433 that is used by SQL Database, or you may be using a proxy server that is not configured properly. Use the same techniques to troubleshoot these difficulties that you would for SQL Server. For more information, see SQL Database Connectivity Troubleshooting Guide and Troubleshooting SQL Database.
Your application must handle general network errors. You may receive general network errors because Windows Azure SQL Database might disconnect users under these circumstances:
- When a connection is idle for an extended period of time
- When a connection consumes an excessive amount of resources or holds onto a transaction for an extended period of time
- If the server is too busy
To improve performance in Windows Azure SQL Database, use the same techniques you would use with SQL Server. For more information, see the following topics:
Windows Azure SQL Database uses a subset of SQL Server error messages. For more information about SQL Server errors, see Errors and Events Reference (Database Engine) in SQL Server Books Online
If you need to recover login names or passwords, contact your service administrator, who can grant you proper access to the server and database. Service administrators can also reset their own passwords using the Windows Azure Management Portal.
SQL Database queries can fail for various reasons – a malformed query, network issues, and so on. Some errors are transient, meaning the problem often goes away by itself. For this subset of errors, it makes sense to retry the query after a short interval. If the query still fails after several retries, you would report an error. Of course, not all errors are transient. SQL Error 102, “Incorrect syntax,” won’t go away no matter how many times you submit the same query. In short, implementing robust retry logic requires some thought. A tabular data stream (TDS) error token is sent prior to disconnecting users, when possible. To improve application experience, we recommend that you implement the retry logic in your SQL Database applications to catch these errors. When an error occurs, re-establish the connection, and then re-execute the failed commands or the query. For more information, see the following links:
Windows Azure SQL Backup and Restore Strategy
Windows Azure SQL Database requires its own backup-and-restore strategy because of the environment and tools available. In many ways the risks have been mediated by the database being in the Microsoft data centers. The tools that we have today cover the other risk factors, however better tools are coming to make the job much easier. Red-gate recently published a free tool for SQL Database backup and restore which can be found here: http://www.red-gate.com/products/dba/sql-azure-backup/.
SQL Data Sync enables you to easily create and schedule bi-directional synchronizations from within the Data Sync web site without the need to write a single line of code. You can find more information here: http://msdn.microsoft.com/en-us/library/windowsazure/hh456371.aspx.
For more information on SQL Database backup and Restore strategies see the following articles:
Windows Azure Caching
Windows Azure Caching comes in two flavors: the Windows Azure Shared Caching and role-based Windows Azure Caching (Preview). Shared Caching is a multitenent Windows Azure service that provides caching services. Windows Azure Caching (Preview) hosts caching on a role by using a portion of the memory from the virtual machines that host your role instances. To troubleshoot Windows Azure Caching, observe the behavior of the cache by checking error codes and catching exceptions. When using role-based Cachineg(Preview),you can also use performance counters. Caching problems generally fall into one of the following categories:
- Quota-related errors - a quota has been exceeded (Shared Caching)
- Throttling - occurs when there is not enough physical memory to support additional cached items
- Eviction - items are forcibly evicted to make room for new items in a way that hurts application performance
- Expiration - expiration times are set too short or long
For more information on quota-related errors, see Understanding Quotas.