I have created a custom fault sequence under /_system/governance/apimgt/customsequences/fault and selected the fault sequence in Fault drop down in API publisher. this fault sequence is never hit when backend returns other than 200 HTTP status code. when would the sequence invoked which selected in "Fault" drop down in API publisher ?
Fault sequence is only hit if anything goes wrong (i.e. exception or error) in the mediation flow. All responses from backend go to out sequence.
Please read https://docs.wso2.com/display/ESB500/Error+Handling for more information about the fault sequence.
If you want to handle responses from backend, you have to write a custom out sequence and do anything you want depending on the status code.
Related
It is best practice to handle such API errors by try and catch or the API response suppose to be like Google, Facebook and Microsoft API call
Google API call example
Facebook API call example
Microsoft API call example
As a general rule, there isn't such a thing as a standard API, so there also isn't a best practice as such either. If you are dealing with multiple APIs within your app, you'll end up having at least a handful of variations in what you check for and how you adapt.
Depending on how terminal the failure is, and where it happens in their processing stack, the HTTP status may be set, and you may also get an HTML, JSON or XML body with more detail (no matter what you thought you might get).
APIs also fail randomly with transient errors, so for your code to work reliably, you probably need a retry loop somewhere.
They also throttle, so some kind of detect/backoff/retry handler would help (details vary per API, as ever).
Psuedocode:
retry loop {
request
check connection (network errors)
check HTTP status code
check body
parse body if valid and extract errors
if terminal failure exit (authentication/authorisation etc)
if throttling backoff
}
We are seeing a random error that seems to be caused by two requests' data getting mixed up. We receive a request for quoting shipping costs on an Order, but the request fails because the requested Order is not accessible by the requesting account. I'm looking for anyone who can provide an inkling on what might be happening here, I haven't found anything on google, the official flask help channels, or SO that looks like what we're experiencing.
We're deployed on AWS, with apache, mod_wsgi, 1 process, 15 threads, about 10 instances.
Here's the code that sends the email:
msg = f"Order ID {self.shipping.order.id} is not valid for this Account {self.user.account_id}"
body = f"Error:<br/>{msg}<br/>Request Data:<br/>{request.data}<br/>Headers:<br/>{request.headers}"
send_email(msg, body, "devops#*******.com")
request_data = None
The problem is that in that scenario we email ourselves with the error and the request data, and the request data we're getting, in many cases, would've never landed in that particular piece of code. It can be a request from the frontend to get the current user's settings, for example, that make no reference to any orders, nevermind trying to get a shipping quote for it.
Comparing the application logs with apache's access_log, we see that, in all cases, we got two requests on the same instance, one requesting the quoting, and another which is the request that is actually getting logged. We don't know whether these two requests are processed by the same thread in rapid succession, or by different threads, but they come so close together that I think the latter is much more probable. We have no way of univocally tying the access_log entries with the application logging, so far, so we don't know which one of the requests is logging the error, but the fact is that we're getting routed to a view that does not correspond to the request's content (i.e., we're not sure whether the quoting request is getting the wrong request object, or if the other one is getting routed to the wrong view).
Another fact that is of interest is that we use graphql, so part of the routing is done after flask/werkzeug do theirs, but the body we get from flask.request at the moment the error shows up does not correspond with the graphql function/mutation that gets executed. But this also happens in views mapped directly through flask. The user is looked up by the flask-login workflow at the very beginning, and it corresponds to the "bad" request (i.e., the one not for quoting).
The actual issue was a bug on one of python-graphql's libraries (promise), not on Flask, werkzeug or apache. It was not the request data that was "moving" to a different thread, but a different thread trying to resolve the promise for a query that was supposed to be handled elsewhere.
I created a service consumer through the wizard, based on a WSDL. Proxy object is generated, all structures and methods are found. Then, I add a logical port through SOAMANAGER - all fine, it pings and the connection works.
I populate the input structure, call my method and get an error: Error during proxy processing (PART UNKNOWN (NULL)). This is a very useless error message to me.
So, I activate all manners of tracing, so I can see what's going on calling and retrieving data. I can see that
My proxy is called correctly
The payload sent TO the service looks correct
The payload received FROM the service is correct. I know this because it's identical to the XML I get back calling the service through other means.
The transformation is empty
Here a screen of (the start of) the returned XML. getRecordsResult set is what I need:
This is the second response, after "conversion":
Nothing about this service has been customized: it's generated straight up through the wizard. I have already deleted and recreated it but no results.
Anyone got any advice on what to do next?
I need to launch the on error sequence o generate a internal error when I receive a soap fault response in my orchestration. Something like throw an exception in Java.
An easy way is to set a filter in each sequence so that, when a fault tag is received, the onError sequence is launched. I guess there must be better ways to do this.
How can I make soap fault responses are treated like an error so that the on error sequence is launched?
This was not straight-forward until WSO2 ESB 4.5.0 (which is the latest release). There is new property introduced "FORCE_ERROR_ON_SOAP_FAULT" to get this done. See this post for a sample configuration.
In your proxy configuration, define the fault sequence..
I have a legacy VB6 application that needs to make asynchronous calls to a web service. The web service provides a search method allows end-users to query a central database and view the results from within the application. I'm using the MSXML2.XMLHTTP to make the requests, and have written a SearchWebService class that encapsulates the web service call and code to handle the response asychronously.
Currently, the SearchWebService raises one of two events to the caller: SearchCompleted and SearchFailed. A SearchCompleted event is raised that contains the search results in a parameter to the event if the call completes successfully. A SearchFailed is raised when any type of failure is detected, which can be anything from an improperly-formatted URL (this is possible because the URL is user-configurable), to low-level network errors such as "Host not found", to HTTP errors such as internal server errors. It returns a error message string to the end-user (which is extracted from the web service response body, if present, or from the HTTP status code text if the response has no body, or translated from the network error code if a network error occurs).
Because of various security requirements, the calling application does not access the web service directly, but instead accesses it through a proxy web server running at the customer site, which in turn accesses the actual web service through via a VPN. However, the SearchWebService doesn't know that the calling application is accessing the web service through a proxy: it's just given a URL and told to make the request. The existence of the proxy is a application-level requirement.
The problem is that from an end-user perspective, it's important that the calling application be able to distinguish between low-level network errors versus HTTP errors from the web service, and to distinguish proxy errors from remote web server errors. For example, the application needs to know if a request failed because the proxy server is down, or because the remote web service that the proxy is accessing is down. An application-specific message needs to be presented to the end-user in each case, such as "Search web service proxy server appears to be down. The proxy server may need to be restarted" versus "The proxy is currently running but the remote web server appears to be unavailable. Please contact (name of person in charge of the remote web server)." I could handle this directly in the SearchWebService class, but it seems wrong to generate these application-specific error messages from such a generic class (and the class might be used in environments that don't require a proxy, where the error messages would no longer make sense).
This distinction is important for troubleshooting: a proxy server problem can usually be resolved by the customer, but a remote web server error has to handled by a third party.
I was thinking one way to handle this would be to have the SearchWebService class detect different types of errors and raise different events in each case. For example, instead of a single SearchFailed event, I could have a NetworkError event for low-level network errors (which would indicate a problem accessing the proxy server), a ConfigurationError event for invalid properties on the SearchWebService class (such as passing an improperly-formatted URL), and a ServiceError for errors that occur on the remote web server (implying that the proxy is working properly but the remote server returned an error).
Now that I think about it, there is also an additional error scenario: it could be possible that the proxy server is running properly, but the remote web server is down, or the proxy server has been misconfigured.
Is the approach of using multiple error events to classify different classes of error a reasonable solution to this problem? For the last scenario (the proxy is running but the remote server cannot be reached), I'm guessing I may have to set up the proxy to return a specific HTTP error code so that client can detect this situation (i.e. something more specific than a 500 response).
Originally I kept the single SearchFailed event and simply added an additional errorCode parameter to the event, but that got messy quickly, especially in cases where there wasn't a logical error code to use (such as if the VB6 raises a "real" error, i.e. if the XMLHTTP class isn't registered).
I think that some ideas I've used with Java exceptions may apply here.
Having a large number of different Exceptions gets pretty messy, yet we need to give enough detail to the user so we don't want to lose information.
Hence I have a small number of specific Exceptions, which I guess would correspond to your Events:
InvalidRequestEvent: Used when the user specifies bad information
TransientErrorEvent: used when there's infrastructure issues when a retry might work.
I tend to work in environments where we have clusters of servers so if a user request hits a dying server then if he resubmits he'll probably get a good one, hence from his perspective a simple retry often works. However sometimes the error is with a service such as the Network or Database and in which case the user needs diagnostic information to report to the helpdesk. Hence we need to decide on the extra information to put into the exception. This is (if I understand you correctly) your question.
In the case of InvalidRequestException we would bet giving some information about the problems with the input. It could be on the lines of "Mismatched parenthese" or "Unknown column CUTSOMER in table ORDER". In the case of TransientErrorException it could be "Proxy server is down".
Now depending upon your exact requirments you may not actually choose to put that text in the Exception, but rather an error number which the presentation layer converts to a locale-specific string (English, French ...).
So either Exception might contain something like this (sorry for that Java syntax, but I hope the idea is clear):
BaseException {
String ErrorText; // the error text itself
// OR if you want to allow for internationaliation
int ErrorCode; // my application specific code, corresponds to text held by the UI
String[] params; // specific parameters to be substitued in the error text
// CUTSOMER and ORDER in my example above
int SystemErrorCode; // If you have an underlying error code it goes here
String SystemErrorText; // any further diagnoistic you might need to give to
// the user so that they can report the problem to the
// help desk.
// OR instead of the text (this is something I've seen done)
int SystemErrorTag; // A unique id for this particular error problem.
// This server systems will label their message in the
// server logs. Users just tell the help desk this number
// they don't need to read detailed server error text.
}