multiple ajax requests giving 504 gateway timeouts - php

Question

I am building a very large pdf book using PHP, I am using ajax to trigger the script. My issue is that because it so big it was timing out, so I decided to break it and recursively call the script several times. I tested this a few weeks back and it was fine. However now I am getting random "504 gateway timeout" issues with some of the ajax calls.
Im not sure where to even begin debugging this as I believed the entire purpose of doing several ajax calls was to prevent this issue. Unfortunately I dont have access to the server as its on a shared hosting package.
<?php $i =1; for($i;$i<=$number_of_pages;$i++) { ?>
<?php if ($i == $number_of_pages) { $last = 1; } else { $last = 0; } ?>
<script>
$(document).ready(function() {
jQuery('.waiting-gif').show();
var number_of_pages = '<?php echo $number_of_pages; ?>';
var build_progress_width = 480/number_of_pages;
var last = '<?php echo $last; ?>';
$.ajax({
url: 'index.php?route=pdfengine/pdfengine/trigger_pdf_gen',
type: 'post',
dataType: 'json',
data: {
pdf_id : '<?php echo $this->request->get['pdf_id']; ?>',
page_number: '<?php echo $i; ?>',
},
beforeSend: function() {
},
complete: function() {},
success: function(json) {
$('.build-progress-green').css('width', build_progress_width);
$('.pdf-build-progress').append('<div class="build-progress-green"></div>');
if (last == '1') {
$.ajax({
url: 'index.php?route=pdfengine/pdfengine/merge_pdfs',
type: 'post',
dataType: 'json',
data: {
pdf_id : '<?php echo $this->request->get['pdf_id']; ?>',
},
beforeSend: function() {},
complete: function() {},
success: function(json) {
var link = document.getElementById('downloadlink');
// Set the link to the json response
link.href = json['download_link'];
$('#downloadlink').attr('download','reads-pdf-id-' + json['pdf_id'] + '.pdf');
// Unhide the link
link.style.display = 'block';
$('#downloadlink').trigger('click');
$('.waiting-gif').hide();
}
});
}
}
});
});
</script>
<?php } ?>
The main function being called via ajax...
public function trigger_pdf_gen() {
if(isset($this->request->post['pdf_id'])) {
$this->load->model('pdfengine/pdfengine');
$pdf_info = $this->model_pdfengine_pdfengine->getPdfInfo($this->request->post['pdf_id']);
$page_number = $this->request->post['page_number'];
$this->session->data['childs_name'] = $pdf_info[0]['childs_name'];
$this->session->data['pdf_id'] = $pdf_info[0]['pdf_id'];
$this->session->data['gift_message'] = $pdf_info[0]['gift_message'];
$double_pages = explode(',',$this->model_pdfengine_pdfengine->getDoublePages($pdf_info[0]['book_path']));
$is_double_page = 0;
foreach ($double_pages as $double_page) {
if ($double_page == $page_number) { $is_double_page = 1; }
}
$this->generate_final_pdf($pdf_info[0]['pdf_id'],$pdf_info[0]['book_path'],$pdf_info[0]['childs_gender'], $page_number,$is_double_page );
$json = array();
$json[] = "<a href='".DIR_FINAL_PDFS_PUBLIC.$pdf_info[0]['pdf_id']."/final-build-".$pdf_info[0]['pdf_id'].".pdf'>The file :)</a>";
$this->response->setOutput(json_encode($json));
}
}
Is it possible this could be a temporary server related issue?

Answer 1

I found a workaround, I wouldnt call it a solution exactly but it does the job.
I scrapped the for loop and forced each trigger of ajax request on a time delay using javascript.
var counter = 1;
trigger_pdf();
var i = setInterval( trigger_pdf, 61000);
function trigger_pdf() {
$.ajax({
url: 'index.php?route=pdfengine/pdfengine/trigger_pdf_gen',
type: 'post',
dataType: 'json',
data: {
pdf_id : '<?php echo $this->request->get['pdf_id']; ?>',
page_number: counter,
},
beforeSend: function() {
},
complete: function() {},
error: function() {
alert('Build failed and timed out, please contact ####');
},
success: function(json) {
$('.build-progress-green').css('width', build_progress_width);
$('.pdf-build-progress').append('<div class="build-progress-green"></div>');
}
});
if(counter == number_of_pages) {
clearInterval(i);
$.ajax({
url: 'index.php?route=pdfengine/pdfengine/merge_pdfs',
type: 'post',
dataType: 'json',
data: {
pdf_id : '<?php echo $this->request->get['pdf_id']; ?>',
},
beforeSend: function() {},
complete: function() {},
success: function(json) {
var link = document.getElementById('downloadlink');
// Set the link to the json response
link.href = json['download_link'];
$('#downloadlink').attr('download','reads-pdf-id-' + json['pdf_id'] + '.pdf');
// Unhide the link
link.style.display = 'block';
$('#downloadlink').trigger('click');
$('.waiting-gif').hide();
}
});
}
counter++;
}