Deno Deploy Bug Promoting To Production Doesnt Enable Queues

Aug 3, 2025 by JurnalWarga.com 61 views

[Bug] Promoting a Deployment to Production Doesn't Enable Queues

Hey guys! Let's dive into a potentially confusing issue I stumbled upon while exploring Deno Deploy, specifically regarding promoting deployments to production and the behavior of queues. As a newcomer to the platform, I wanted to share my experience and hopefully get some clarity on whether this is intended behavior or a bug.

Problem Description

So, here's the deal: I was a bit unsure about the difference between "preview deployments" that have been "promoted to production" and regular "production deployments." It seems to me that the queues feature is only available if you initially deploy using the --prod flag, effectively marking it as a production deployment from the get-go. If you deploy without the --prod flag and then promote it via the Deno Deploy web UI, the queues don't seem to kick in. This is what I saw:

Queues are not supported for preview deployments. Enqueued messages will be dropped.

This message kept popping up even after I promoted the deployment, which was quite puzzling.

When working with Deno Deploy, understanding the nuances of preview versus production deployments is crucial, especially when utilizing features like queues. The initial confusion arose from the behavior observed after promoting a preview deployment to production via the Deno Deploy web UI. Despite the promotion, the queues feature remained disabled, indicated by the persistent message "Queues are not supported for preview deployments. Enqueued messages will be dropped." This observation raised questions about the intended functionality and the differentiation between deployments initiated with the --prod flag and those promoted through the UI. To effectively troubleshoot and clarify this behavior, a series of steps were undertaken to reproduce the issue consistently.

Reproducing the problem involved deploying a simple script designed to interact with Deno Deploy's queueing system. This script, derived from a tutorial on webhook processing, served as a practical test case for evaluating queue functionality. The deployment process began without the --prod flag, intentionally creating a preview deployment. Subsequently, this deployment was promoted to production using the Deno Deploy dashboard. Despite this promotion, the queues feature remained inactive, suggesting a discrepancy between the expected and actual outcomes. This discrepancy highlights the importance of clear documentation and consistent behavior across different deployment scenarios. Furthermore, it underscores the need for developers to fully grasp the implications of deployment flags and promotion processes to ensure that applications function as intended in production environments. The observed behavior prompted a deeper investigation into the underlying mechanisms governing deployment types and their impact on feature availability, ultimately leading to a more comprehensive understanding of Deno Deploy's capabilities and limitations. This iterative process of experimentation and observation is essential for navigating complex platforms and optimizing application deployment strategies.

Understanding the behavior of queues in Deno Deploy is essential for developers aiming to leverage asynchronous message processing in their applications. The core issue lies in the apparent distinction between deployments initiated as production deployments using the --prod flag and those that are promoted to production via the Deno Deploy web UI. The observed discrepancy indicates that promoting a preview deployment might not fully activate all features associated with production environments, specifically the queues functionality. This distinction can lead to unexpected behavior, especially for developers who assume that promoting a deployment is equivalent to deploying with the --prod flag from the outset. The persistent message, "Queues are not supported for preview deployments. Enqueued messages will be dropped," even after promotion, highlights this inconsistency. To fully utilize queues, it appears necessary to deploy with the --prod flag initially, ensuring that the deployment is recognized as a production environment from the start. This requirement underscores the importance of carefully planning deployment strategies and understanding the implications of each deployment method. The behavior also suggests that the promotion process might not trigger all the necessary backend configurations to enable features like queues, which are critical for building scalable and responsive applications. Therefore, developers should be aware of this potential pitfall and adopt a deployment approach that aligns with their application's requirements, particularly concerning asynchronous message processing and queue management. This awareness helps in avoiding unexpected issues and ensures a smoother transition to production environments.

Steps to Reproduce

To illustrate the issue, I followed these steps:

Create a simple script: I used a script adapted from the Deno Deploy documentation on webhook processing. This script sets up a queue listener and an HTTP server to enqueue messages.

const kv = await Deno.openKv();

kv.listenQueue(async (message) => {
  console.log("LISTENER GOT MESSAGE:", message);
  await kv.set(["queue", Date.now()], message);
});

Deno.serve(async (req: Request) => {
    if (req.method === "POST") {
        const payload = await req.json();
        console.log("Received webhook with payload:", payload);
        await kv.enqueue(payload);
        return new Response("", { status: 200 })
    } else {
        const iter = kv.list<string>({ prefix: ["queue"] });
        const stuff = [];
        for await (const res of iter) stuff.push({
            timestamp: res.key[1],
            payload: res.value,
        });
        return new Response(JSON.stringify(stuff, null, 2));
    }
});

Deploy without the --prod flag: I deployed the script using deployctl deploy without the --prod flag. This created a preview deployment.
Promote the deployment to production from the web UI: I navigated to my project on Deno Deploy dashboard, clicked the three dots next to the deployment, and selected Promote to production. Despite this, the logs continued to show:
```
Queues are not supported for preview deployments. Enqueued messages will be dropped.
```
And, of course, the queue feature didn't work as expected.

To effectively demonstrate the problem, a detailed procedure was followed, emphasizing the nuances of deploying and promoting applications within Deno Deploy. The initial step involved creating a simple yet functional TypeScript script, adapted from the official Deno Deploy documentation on webhook processing. This script was designed to interact with Deno Deploy's queueing system, establishing a queue listener and an HTTP server capable of enqueuing messages. This setup provided a practical test case for evaluating the behavior of queues in different deployment scenarios. The core functionality of the script included opening a connection to Deno KV, setting up a listener for incoming queue messages, and defining an HTTP endpoint to handle POST requests by enqueuing payloads. Additionally, the script provided a read endpoint to list the contents of the queue, facilitating verification of message processing. This comprehensive functionality made the script an ideal tool for examining the activation of queues after deployment promotion. The decision to use this specific script stemmed from its direct relevance to the queues feature and its ability to clearly demonstrate whether messages were being processed as expected. By encapsulating the essential elements of queue interaction within a concise script, the reproduction steps could focus on the deployment and promotion aspects of the issue, ensuring a controlled and replicable test environment. This meticulous approach to script development was crucial for isolating the problem and accurately assessing the behavior of Deno Deploy in different deployment configurations.

Deploying the script without the --prod flag was a crucial step in reproducing the issue. This action intentionally created a preview deployment, setting the stage for observing the behavior of queues after promotion. The command deployctl deploy was used, omitting the --prod flag, which resulted in the deployment being categorized as a preview rather than a production environment. This distinction is significant because Deno Deploy treats preview and production deployments differently, particularly in terms of feature availability and resource allocation. Preview deployments are typically used for testing and staging purposes, while production deployments are intended for live, user-facing applications. By deploying without the --prod flag, the script was initially configured within the preview environment, allowing for a direct comparison of functionality before and after promotion. This step is essential for understanding whether the promotion process fully activates all production-level features, such as queues. The deployment process itself was straightforward, involving the use of Deno's command-line tools to upload and deploy the script to the Deno Deploy platform. However, the omission of the --prod flag at this stage was a deliberate choice, designed to highlight the specific issue under investigation. The subsequent promotion of the deployment from the web UI served as the pivotal point in the reproduction process, allowing for a clear observation of whether the queues feature would be enabled as expected. This methodical approach to deployment and promotion was key to uncovering the discrepancy in behavior between preview and production environments and understanding its impact on queue functionality.

After deploying the script as a preview, the next critical step was to promote the deployment to production using the Deno Deploy web UI. This action is designed to transition the deployment from a testing environment to a live, production-ready state. The process involved navigating to the Deno Deploy dashboard, selecting the project, and locating the preview deployment that was previously created. By clicking the three dots next to the deployment, a menu appeared, offering the option to "Promote to production." Selecting this option initiated the promotion process, which typically involves updating the deployment's configuration and routing traffic to the new version. The expectation was that promoting the deployment would activate all features associated with a production environment, including the queues functionality. However, despite the successful promotion, the logs continued to display the message "Queues are not supported for preview deployments. Enqueued messages will be dropped." This persistent message indicated that the queues feature had not been enabled, even after the deployment was officially promoted to production. This discrepancy formed the core of the issue being investigated, suggesting that the promotion process might not fully replicate the effects of deploying with the --prod flag from the beginning. The consistent failure to activate queues after promotion highlighted the potential for confusion among developers who might assume that promoting a deployment is equivalent to deploying directly to production. This observation underscored the importance of clearly understanding the nuances of deployment types and their impact on feature availability within the Deno Deploy platform. The subsequent analysis focused on identifying the underlying reasons for this behavior and proposing potential solutions to ensure a more consistent and predictable deployment experience.

Expected Behavior

My expectation, perhaps wrongly, was that the 'queues' feature would be enabled once a deployment was promoted to production. This seemed like a logical progression – a preview deployment being elevated to a full-fledged production deployment, with all the bells and whistles (including queues) activated.

The initial assumption was that promoting a deployment to production would seamlessly enable all associated features, including queues, mirroring the behavior of deploying directly with the --prod flag. This expectation stemmed from the intuitive understanding that a promoted deployment should transition fully into a production environment, equipped with the same capabilities and functionalities as one deployed as production from the outset. The logic behind this assumption is that the promotion process should essentially replicate the steps taken during a production deployment, ensuring that all necessary configurations and services are activated. However, the observed behavior deviated from this expectation, leading to a closer examination of the underlying mechanics of deployment promotion. The anticipation of queue activation was particularly relevant given the asynchronous nature of queue-based processing, which is often crucial for building scalable and responsive applications. The failure to activate queues after promotion suggested that the promotion process might not fully trigger the necessary backend configurations or services required for this feature. This discrepancy highlighted a potential gap in the user experience, where the expected behavior differed significantly from the actual outcome. As a result, the investigation focused on understanding why queues were not being enabled and identifying the steps needed to ensure that promoted deployments behave consistently with deployments initiated as production.

Environment

Here's my environment setup:

% deno --version
deno 2.4.2 (stable, release, aarch64-apple-darwin)
v8 13.7.152.14-rusty
typescript 5.8.3

% deployctl --version
deployctl 1.13.1

This information is crucial for anyone trying to reproduce the issue or pinpoint any environment-specific factors.

Providing the environment details is a critical aspect of reporting issues, as it helps in reproducing the problem and identifying any potential environment-specific factors. The environment information includes the versions of Deno, V8, TypeScript, and Deployctl used during the testing. Specifically, Deno version 2.4.2, running on a stable release with an aarch64-apple-darwin architecture, indicates the core runtime environment. The V8 version 13.7.152.14-rusty provides details about the JavaScript engine, while TypeScript version 5.8.3 specifies the version of the TypeScript compiler. Additionally, the Deployctl version 1.13.1 is crucial as it represents the deployment tool used to interact with the Deno Deploy platform. This combination of versions offers a comprehensive snapshot of the development and deployment environment, enabling others to replicate the exact conditions under which the issue was observed. By including this information, the report ensures that any discrepancies or behaviors can be accurately attributed to the software versions in use. This level of detail is invaluable for debugging and troubleshooting, as it narrows down the potential causes of the issue and facilitates targeted investigations. Furthermore, providing the environment information underscores the importance of consistency and reproducibility in software development and deployment, ensuring that issues can be effectively addressed and resolved.

Possible Solution

The queues feature seems to work fine if you deploy initially as a production deployment using the --prod flag. If this behavior is intended, perhaps a small note could be added to the