Hi, i have a big issue with my multitenant applica...

# server

[Jeremy Rouet]

Hi, i have a big issue with my multitenant application in Ktor. I store the context in the ThreadLocal with the "asContextElement". please find un attachement. But sometime, when the function is suspended the context is lost... Any idea ?

import io.ktor.application.ApplicationCall
import io.ktor.request.header
import kotlinx.coroutines.asContextElement

const val TENANT_HEADER_VALUE = "tenantID";
const val TENANT_HEADER_URL_VALUE = "tenantURL";
const val CLIENT_HEADER_URL_VALUE = "clientURL";
const val TENANTID_DEFAULT_VALUE = "master"

object ContextManager {
    private val context = ThreadLocal<Context>();

    /**
     * Register a request in the context
     */
    fun registerCall(call: ApplicationCall) {

        var requestContext = getContext();

        var tenantID = call.request.header(TENANT_HEADER_VALUE);
        LOGGER.trace("Find ${tenantID} in ${call.request.headers}")
        if (tenantID == null || tenantID.isEmpty()) {
            tenantID = TENANTID_DEFAULT_VALUE;
        }
        requestContext.tenantID = tenantID;
        requestContext.tenantUrl = call.request.header(TENANT_HEADER_URL_VALUE).toString();
        requestContext.clientURL = call.request.header(CLIENT_HEADER_URL_VALUE).toString();


        setContext(requestContext);
    }

    fun setContext(context: Context) {
        this.context.set(context);
        this.context.asContextElement(context);
    }

    fun getContext(): Context {
        var requestContext = context.get();
        if (requestContext == null) {
            requestContext = Context()
        }
        return requestContext;
    }

    fun declareContext(tenantID: String, tenantUrl: String = "", clientURL: String = "") {
        val requestContext = getContext();
        requestContext.tenantUrl = tenantUrl;
        requestContext.tenantID = tenantID;
        requestContext.clientURL = clientURL;
    }

}

class Context {
    var tenantID = TENANTID_DEFAULT_VALUE;
    var tenantUrl = "";
    var clientURL = "";
}

[cab]

ktor uses thread pool, which means your thread local will return different values between calls.

[Jeremy Rouet]

yes but the "asContext" keep the context?

[cab]

i am not sure that anything is kept. like, each time a new worker spawns, all plugins get reinitialized for it, so my guess is nope.
but let me fetch docs.

[cab]

also to test my theory you can log current thread name and send a barrage of calls to server. and see if context loss is correlated with different threads executing calls.

[cab]

oh, and yeah, almost forgot

[cab]

before async and after it you might be executing in different threads.

[Jeremy Rouet]

so it's not possible to create multitenant application with ktor? Maybe I missundertood, but with asContextElement, the ThreadLocal is supposed to be maintain in different thread? https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/java.lang.-thread-local/as-context-element.html

[David Eriksson]

You shouldn't mix thread local with coroutines.

[David Eriksson]

But of course asContextElement should work 🙂

[David Eriksson]

I think you always need to access the context as threadLocalContext.asContextElement()
Lots of things called context in your example 🙂

[Jeremy Rouet]

Sure, too many "context" in my code. If we cannot use coroutine and thread local , how can create a multi-tenant API?

[Jeremy Rouet]

Feature of Ktor use threadLocalContext like https://ktor.io/servers/features/call-logging.html