Add app

Dockerfile

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+FROM python:3.9
+
+WORKDIR /code
+
+COPY ./requirements.txt /code/requirements.txt
+
+RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt
+
+COPY . .
+
+EXPOSE 7860
+
+ENTRYPOINT ["/bin/sh", "-c"]
+CMD ["shiny run app.py --host 0.0.0.0 --port 7860"]
+

app.py

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+import starlette.responses
+
+from shiny import *
+
+app_ui = ui.page_fluid(
+    ui.markdown(
+        """
+        ## Sticky load balancing test
+
+        The purpose of this app is to determine if HTTP requests made by the client are
+        correctly routed back to the same Python process where the session resides. It
+        is only useful for testing deployments that load balance traffic across more
+        than one Python process.
+
+        If this test fails, it means that sticky load balancing is not working, and
+        certain Shiny functionality (like file upload/download or server-side selectize)
+        are likely to randomly fail.
+        """
+    ),
+    ui.tags.div(
+        {"class": "card"},
+        ui.tags.div(
+            {"class": "card-body font-monospace"},
+            ui.tags.div("Attempts: ", ui.tags.span("0", id="count")),
+            ui.tags.div("Status: ", ui.tags.span(id="status")),
+            ui.output_ui("out"),
+        ),
+    ),
+)
+
+
+def server(input: Inputs, output: Outputs, session: Session):
+    @output
+    @render.ui
+    def out():
+        # Register a dynamic route for the client to try to connect to.
+        # It does nothing, just the 200 status code is all that the client
+        # will care about.
+        url = session.dynamic_route(
+            "test",
+            lambda req: starlette.responses.PlainTextResponse(
+                "OK", headers={"Cache-Control": "no-cache"}
+            ),
+        )
+
+        # Send JS code to the client to repeatedly hit the dynamic route.
+        # It will succeed if and only if we reach the correct Python
+        # process.
+        return ui.tags.script(
+            f"""
+            const url = "{url}";
+            const count_el = document.getElementById("count");
+            const status_el = document.getElementById("status");
+            let count = 0;
+            async function check_url() {{
+                count_el.innerHTML = ++count;
+                try {{
+                    const resp = await fetch(url);
+                    if (!resp.ok) {{
+                        status_el.innerHTML = "Failure!";
+                        return;
+                    }} else {{
+                        status_el.innerHTML = "In progress";
+                    }}
+                }} catch(e) {{
+                    status_el.innerHTML = "Failure!";
+                    return;
+                }}
+
+                if (count === 100) {{
+                    status_el.innerHTML = "Test complete";
+                    return;
+                }}
+
+                setTimeout(check_url, 10);
+            }}
+            check_url();
+            """
+        )
+
+
+app = App(app_ui, server)

requirements.txt

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+shiny