更新：我在下面添加了解决方案

问题

一些背景知识：我正在Ubuntu精确服务器上运行Shiny服务器v1.5。基本上，我有一个rmarkdown页面，该页面允许用户使用一些参数进行播放，然后具有一个下载按钮，该按钮使用闪亮的格式生成文档，如下所示：

```{r,echo=FALSE}
downloadHandler(
  filename = "report.pdf",
  content = function(file) {
    knitr::knit2pdf("report.Rnw",envir=environment())
    file.rename(normalizePath('report.pdf'), file)
  }
)
```

Shiny应用程序在我的本地计算机上运行良好，但在服务器上崩溃。更具体地说，r markdown网页工作正常，但是一旦我单击下载按钮，该应用程序将在30秒后崩溃。服务器日志指示套接字超时错误：

[2016-02-24 03:38:52.240] [INFO] shiny-server - Starting listener on 0.0.0.0:3838
[2016-02-24 03:49:30.183] [ERROR] shiny-server - Uncaught exception: Error: socket hang up
[2016-02-24 03:49:30.184] [ERROR] shiny-server - Error: socket hang up
    at createHangUpError (_http_client.js:215:15)
    at Socket.socketCloseListener (_http_client.js:247:23)
    at Socket.emit (events.js:129:20)
    at TCP.close (net.js:485:12)
[2016-02-24 03:49:30.184] [INFO] shiny-server - Stopping listener on 0.0.0.0:3838
[2016-02-24 03:49:30.185] [INFO] shiny-server - Shutting down worker processes (with notification)
/opt/shiny-server/lib/main.js:364
  throw err;
        ^
Error: socket hang up
    at createHangUpError (_http_client.js:215:15)
    at Socket.socketCloseListener (_http_client.js:247:23)
    at Socket.emit (events.js:129:20)
    at TCP.close (net.js:485:12)

该pdf生成时间很长（大约五分钟），所以我怀疑我错过了某个地方的超时参数。这是我在闪亮的配置中所做的：

run_as shiny;
app_init_timeout 999999;
app_idle_timeout 999999;

# Define a server that listens on port 3838
server {
  listen 3838;
  ....
}

...但无济于事，因为我仍然遇到错误。任何建议将不胜感激！

解决方案

正如@daattali所提到的，在downloadButton中不能花费那么长时间，更改服务器设置不会对此进行任何更改。因此，我最终将生成和下载功能分为两部分，如下所示：

```{r, echo=FALSE}
shinyApp(
  ui = fluidPage(
    fluidRow(
      column(2,
        conditionalPanel(
          condition = "!$('makeReport').hasClass('shiny-busy')",
          actionButton("makeReport","Generate Report",icon=icon("file"))
        )
      ),
      column(4,
      conditionalPanel(
        condition = "!$('makeReport').hasClass('shiny-busy')",
        uiOutput("downloadButton")
        #downloadButton("downloadReport", "Download Report")
      )
      )
    )
  ),
  server = function(input, output) {
    output$download_button <- renderUI({
        downloadButton("downloadReport", "Download Results")
     })
    makeReportAction <- eventReactive(input$makeReport, {
        ...
        knitr::knit2pdf("report.Rnw",envir=globalenv())
    })
    output$downloadButton <- renderUI({
      makeReportAction() #only appear after first click on generate
      downloadButton("downloadReport", "Download Report")
    })
    output$downloadReport <- downloadHandler(
      filename = "report.pdf",
      content = function(file) {
        cat(paste("Does the pdf exist?",file.exists("report.pdf")))
        file.rename(normalizePath('report.pdf'), file)
      }
    )
  }
)
```