Never Ending Security

It starts all here

Documentation on building a HTTPS stack in AWS with HAProxy

Guidelines for HAProxy termination in AWS

Document status

NOT READY $Revision: $ @ 2015-04-17 09:04 PDT
Author Julien Vehent Review CloudOps

Table of contents

  • 1   Summary & Scope
  • 2   Architecture
  • 3   PROXY protocol between ELB and HAProxy
    • 3.1   ELB Configuration
    • 3.2   HAProxy frontend
    • 3.3   SSL/TLS Configuration
    • 3.4   Healthchecks between ELB and HAProxy
  • 4   ELB Logging
  • 5   HAProxy Logging
    • 5.1   Unique request ID
    • 5.2   Capturing headers and cookies
    • 5.3   Logging in a separate frontend
  • 6   Rate limiting & DDoS protection
    • 6.1   Automated rate limiting
    • 6.2   Querying tables state in real time
    • 6.3   Blacklists & Whitelists
    • 6.4   Protect against slow clients (Slowloris attack)
  • 7   URL filtering with ACLs
    • 7.1   Filtering URL parameters on GET requests
    • 7.2   Filtering payloads on POST requests
    • 7.3   Marking instead of blocking
  • 8   HAProxy management
    • 8.1   Enabling the stat socket
    • 8.2   Collecting statistics
    • 8.3   Analyzing errors
    • 8.4   Parsing performance metrics from the logs
    • 8.5   Soft reload
  • 9   Full HAProxy configuration
  • 10   Building process
    • 10.1   Static build
    • 10.2   Dynamic build
    • 10.3   RPM build

1   Summary & Scope

This document explains how HAProxy and Elastic Load Balancer can be used in Amazon Web Services to provide performant and secure termination of traffic to an API service. The goal is to provide the following features:

  • DDoS Protection: we use HAProxy to mitigate low to medium DDoS attacks, with sane limits and custom blacklist.
  • Application firewall: we perform a first level of filtering in HAProxy, that protects NodeJS against all sorts of attack, known and to come. This will be done by inserting a set of regexes in HAProxy ACLs, that get updated when the application routes are updated. Note that managing these ACLs will not impact uptime, or require redeployment.
  • SSL/TLS: ELBs support the PROXY protocol, and so does HAProxy, which allows us to proxy the tcp connection to HAProxy. It gives us better TLS, backed by OpenSSL, at the cost of managing the TLS keys on the HAProxy instances.
  • Logging: ELBs have limited support for logging. HAProxy, however, has excellent logging for TCP, SSL and HTTPS. We leverage the flexibility of HAProxy’s logging to improve our DDoS detection capabilities. We also want to uniquely identify requests in HAProxy and NodeJS, and correlate events, using a unique-id.

2   Architecture

Below is our target setup:

architecture diagram

3   PROXY protocol between ELB and HAProxy

This configuration uses an Elastic Load Balancer in TCP mode, with PROXY protocol enabled. The PROXY protocol adds a string at the beginning of the TCP payload that is passed to the backend. This string contains the IP of the client that connected to the ELB, which allows HAProxy to feed its internal state with this information, and act as if it had a direct TCP connection to the client.

For more information on the PROXY protocol, see

First, we need to create an ELB, and enable a TCP listener on port 443 that supports the PROXY protocol. The ELB will not decipher the SSL, but instead pass the entire TCP payload down to Haproxy.

3.1   ELB Configuration

PROXY protocol support must be enabled on the ELB.

$ ./elb-describe-lb-policy-types -I AKIA... -S Ww1... --region us-east-1
POLICY_TYPE  ProxyProtocolPolicyType    Policy that controls whether to include the
                                        IP address and port of the originating request
                                        for TCP messages. This policy operates on
                                        TCP/SSL listeners only

The policy name we want to enable is ProxyProtocolPolicyType. We need the load balancer name for that, and the following command:

$ ./elb-create-lb-policy elb123-testproxyprotocol \
--policy-name EnableProxyProtocol \
--policy-type ProxyProtocolPolicyType \
--attribute "name=ProxyProtocol, value=true" \
-I AKIA... -S Ww1... --region us-east-1

OK-Creating LoadBalancer Policy

$ ./elb-set-lb-policies-for-backend-server elb123-testproxyprotocol \
--policy-names EnableProxyProtocol \
--instance-port 443 \
-I AKIA... -S Ww1... --region us-east-1

OK-Setting Policies

Now configure a listener on TCP/443 on that ELB, that points to TCP/443 on the HAProxy instance. On the instance side, make sure that your security group accepts traffic from the ELB security group on port 443.

3.2   HAProxy frontend

The HAProxy frontend listens on port 443 with a SSL configuration, as follow:

frontend https
        bind accept-proxy ssl ......

Note the accept-proxy parameter of the bind command. This option tells HAProxy that whatever sits in front of it will append the PROXY header to TCP payloads.

3.3   SSL/TLS Configuration

HAProxy takes a SSL configuration on the bind line directly. The configuration requires a set of certificates and private key, and a ciphersuite.


Unlike most servers (Apache, Nginx, …), HAProxy takes certificates and keys into a single file, here named bundle.pem. In this file are concatenated the server private key, the server public certificate, the CA intermediate certificate (if any) and a DH parameter (if any). For more information on DH parameters, see .

In the sample below, components of bundle.pem are concatenated as follow:

  • client certificate signed by CA XYZ
  • client private key
  • public DH parameter (2048 bits)
  • intermediate certificate of CA XYZ

The rest of the bind line is a ciphersuite, taken from .

We can verify the configuration using cipherscan. Below is the expected output for our configuration:

$ ./cipherscan
prio  ciphersuite                  protocols                    pfs_keysize
1     ECDHE-RSA-AES128-GCM-SHA256  SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
2     ECDHE-RSA-AES256-GCM-SHA384  SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
3     DHE-RSA-AES128-GCM-SHA256    SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
4     DHE-RSA-AES256-GCM-SHA384    SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
5     ECDHE-RSA-AES128-SHA256      SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
6     ECDHE-RSA-AES128-SHA         SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
7     ECDHE-RSA-AES256-SHA384      SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
8     ECDHE-RSA-AES256-SHA         SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
9     DHE-RSA-AES128-SHA256        SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
10    DHE-RSA-AES128-SHA           SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
11    DHE-RSA-AES256-SHA256        SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
12    DHE-RSA-AES256-SHA           SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
13    AES128-GCM-SHA256            SSLv3,TLSv1,TLSv1.1,TLSv1.2
14    AES256-GCM-SHA384            SSLv3,TLSv1,TLSv1.1,TLSv1.2
15    ECDHE-RSA-RC4-SHA            SSLv3,TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
16    AES128-SHA256                SSLv3,TLSv1,TLSv1.1,TLSv1.2
17    AES128-SHA                   SSLv3,TLSv1,TLSv1.1,TLSv1.2
18    AES256-SHA256                SSLv3,TLSv1,TLSv1.1,TLSv1.2
19    AES256-SHA                   SSLv3,TLSv1,TLSv1.1,TLSv1.2
20    RC4-SHA                      SSLv3,TLSv1,TLSv1.1,TLSv1.2
21    DHE-RSA-CAMELLIA256-SHA      SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
22    CAMELLIA256-SHA              SSLv3,TLSv1,TLSv1.1,TLSv1.2
23    DHE-RSA-CAMELLIA128-SHA      SSLv3,TLSv1,TLSv1.1,TLSv1.2  DH,2048bits
24    CAMELLIA128-SHA              SSLv3,TLSv1,TLSv1.1,TLSv1.2

3.4   Healthchecks between ELB and HAProxy

As of writing of this document, it appears that ELBs do not use the proxy protocol when running healthchecks against an instance. As a result, these healthchecks cannot be handled by the https frontend, because HAProxy will fail when looking for a PROXY header that isn’t there.

The workaround is to create a secondary frontend in HAProxy that is entirely dedicated to answering healthchecks from the ELB.

The configuration below uses the monitor option to check the health of the nodejs backend. If more than one server is alive in that backend, then our health frontend will return 200 OK. If no server is alive, a 503 will be returned. All the ELB has to do is to query the URL athttp://haproxy_host:34180/haproxy_status . To reduce the overhead, we also disable SSL on the health frontend.

# frontend used to return health status without requiring SSL
frontend health
        bind      # 34180 means EALTH ;)
        # create a status URI in /haproxy_status that will return
        # a 200 is backend is healthy, and 503 if it isn't. This
        # URI is queried by the ELB.
        acl backend_dead nbsrv(nodejs) lt 1
        monitor-uri /haproxy_status
        monitor fail if backend_dead

(note: we could also use ACLs in HAProxy to only expect the PROXY header on certain source IPs, but the approach of a dedicated health frontend seems cleaner)

4   ELB Logging


5   HAProxy Logging

HAProxy supports custom log format, which we want here, as opposed to default log format, in order to capture TCP, SSL and HTTP information on a single line.

For our logging, we want the following:

  1. TCP/IP logs first, such that these are always present, even if HAProxy cuts the connection before processing the SSL or HTTP traffic
  2. SSL information
  3. HTTP information
log-format [%pid]\ [%Ts.%ms]\ %ac/%fc/%bc/%bq/%sc/%sq/%rc\ %Tq/%Tw/%Tc/%Tr/%Tt\ %tsc\ %ci:%cp\ %fi:%fp\ %si:%sp\ %ft\ %sslc\ %sslv\ %{+Q}r\ %ST\ %b:%s\ "%CC"\ "%hr"\ "%CS"\ "%hs"\ req_size=%U\ resp_size=%B

The format above will generate:

Mar 14 17:14:51 localhost haproxy[14887]: [14887] [1394817291.250] 10/5/2/0/3/0/0 48/0/0/624/672 ---- logger - - "GET /v1/ HTTP/1.0" 404 fxa-nodejs:nodejs1 "-" "{||ApacheBench/2.3|over-100-active-connections,over-100-connections-in-10-seconds,high-error-rate,high-request-rate,|47B4176E:8B75_0A977AE4:01BB_5323390B_31E0:3A27}" "-" "" ireq_size=592 resp_size=787

The log-format contains very detailed information on the connection itself, but also on the state of haproxy itself. Below is a description of the fields we used in our custom log format.

  • %pid: process ID of HAProxy
  • %Ts.%ms: unix timestamp + milliseconds
  • %ac: total number of concurrent connections
  • %fc: total number of concurrent connections on the frontend
  • %bc: total number of concurrent connections on the backend
  • %bq: queue size of the backend
  • %sc: total number of concurrent connections on the server
  • %sq: queue size of the server
  • %rc: connection retries to the server
  • %Tq: total time to get the client request (HTTP mode only)
  • %Tw: total time spent in the queues waiting for a connection slot
  • %Tc: total time to establish the TCP connection to the server
  • %Tr: server response time (HTTP mode only)
  • %Tt: total session duration time, between the moment the proxy accepted it and the moment both ends were closed.
  • %tsc: termination state (see 8.5. Session state at disconnection)
  • %ci:%cp: client IP and Port
  • %fi:%fp: frontend IP and Port
  • %si:%sp: server IP and Port
  • %ft: transport type of the frontend (with a ~ suffix for SSL)
  • %sslc %sslv: SSL cipher and version
  • %{+Q}r: HTTP request, between double quotes
  • %ST: HTTP status code
  • %b:%s: backend name and server name
  • %CC: captured request cookies
  • %hr: captured request headers
  • %CS: captured response cookies
  • %hs: captured response headers
  • %U: bytes read from the client (request size)
  • %B: bytes read from server to client (response size)

For more details on the available logging variables, see the HAProxy configuration, under 8.2.4. Custom log format.

5.1   Unique request ID

Tracking requests across multiple servers can be problematic, because the chain of events triggered by a request on the frontend are not tied to each other. HAProxy has a simple mechanism to insert a unique identifier to incoming requests, in the form of an ID inserted in the request headers, and passed to the backend server. This ID can then be logged by the backend server, and passed on to the next step. In a largely distributed environment, the unique ID makes tracking requests propagation a lot easier.

The unique ID is declared on the HTTPS frontend as follow:

# Insert a unique request identifier is the headers of the request
# passed to the backend
unique-id-format %{+X}o\ %ci:%cp_%fi:%fp_%Ts_%rt:%pid
unique-id-header X-Unique-ID

This will add an ID that is composed of hexadecimal variables, taken from the client IP and port, frontend IP and port, timestamp, request counter and PID. An example of generated ID is485B7525:CB2F_0A977AE4:01BB_5319CB0C_000D:27C0.

The Unique ID is added to the request headers passed to the backend in the X-Unique-ID header. We will also capture it in the logs, as a request header.

GET / HTTP/1.1
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Cache-Control: max-age=0
X-Unique-ID: 485B7525:CB70_0A977AE4:01BB_5319CD3F_0163:27C0

5.2   Capturing headers and cookies

In the log format, we defined fields for the request and response headers and cookies. But, by default, this fields will show empty in the logs. In order to log headers and cookies, the capture parameters must be set in the frontend.

Here is how we can capture headers sent by the client in the HTTP request.

    capture request header Referrer len 64
capture request header Content-Length len 10
    capture request header User-Agent len 64

Cookies can be captures the same way:

capture cookie mycookie123=  len 32

HAProxy will also add custom headers to the request, before passing it to the backend. However, added headers don’t get logged, because the addition happens after the capture operation. To fix this issue, we are going to create a new frontend dedicated to logging.

5.3   Logging in a separate frontend

During processing of the request, we added custom headers, and we want these headers to appear in the logs. One solution is to route all the request to a secondary frontend that only does logging, and blocking or forwarding.

Classic setup:

 request        +--------------+       +---------------+
+-------------->|frontend      |+----->|backend        |      +---------+
                |   fxa-https  |       |    fxa-nodejs |+---->|         |
                +--------------+       +---------------+      | NodeJS  |
                                                              |         |

Setup with separate logging frontend:

                {no logging}
 request        +--------------+       +---------------+
+-------------->|frontend      |       |backend        |      +---------+
                |   fxa-https  |       |    fxa-nodejs |+---->|         |
                +--------------+       +---------------+      | NodeJS  |
                       +                     ^                |         |
                       |                     |                +---------+
                       |                     |
                +------v-------+       +-----+--------+
                |backend       |+----->|frontend      |
                |     logger   |       |   logger     |
                +--------------+       +--------------+

At the end of the configuration of frontend fxa-https, instead of sending requests to backend fxa-nodejs, we send them to backend logger.

frontend fxa-https
        # Don't log here, log into logger frontend
        no log
        default_backend logger

Then we declare a backend and a frontend for logger:

backend logger
        server localhost localhost:55555 send-proxy

# frontend use to log acl activity
frontend logger
        bind localhost:55555 accept-proxy


        capture request header Referrer len 64
        capture request header Content-Length len 10
        capture request header User-Agent len 64
        capture request header X-Haproxy-ACL len 256
        capture request header X-Unique-ID len 64

        # if previous ACL didn't pass and aren't whitelisted
        acl whitelisted req.fhdr(X-Haproxy-ACL) -m beg whitelisted,
        acl fail-validation req.fhdr(X-Haproxy-ACL) -m found
        http-request deny if !whitelisted fail-validation

        default_backend fxa-nodejs

Note the use of send-proxy and accept-proxy between the logger backend and frontend, allowing to keep the information about the client IP.

Isn’t this slow and inefficient?

Well, obviously, routing request through HAProxy twice isn’t the most elegant way of proxying. But in practice, this approach adds minimal overhead. Linux and HAProxy support TCP splicing, which provides zero-copy transfer of data between TCP sockets. When HAProxy forward the request to the logger socket, there is, in fact, no transfer of data at the kernel level. Benchmark it, it’s fast!

6   Rate limiting & DDoS protection

One of the particularity of operating an infrastructure in AWS, is that control over the network is very limited. Techniques such as BGP blackholing are not available. And visibility over the layer 3 (IP) and 4 (TCP) is reduced. Building protection against DDoS means that we need to block traffic further down the stack, which consumes more resources. This is the main motivation for using ELBs in TCP mode with the PROXY protocol: it gives HAProxy low-level access to the TCP connection, and visibility of the client IP before parsing HTTP headers (like you would traditionally do with X-Forwarded-For).

ELBs have limited resources, but simplify the management of public IPs in AWS. By offloading the SSL & HTTP processing to HAProxy, we reduce the pressure on ELB, while conserving the ability to manage the public endpoints through it.

HAProxy maintains tons of detailed information on connections. One can use this information to accept, block or route connections. In the following section, we will discuss the use of ACLs and stick-tables to block clients that do not respect sane limits.

6.1   Automated rate limiting

The configuration below enable counters to track connections in a table where the key is the source IP of the client:

# Define a table that will store IPs associated with counters
stick-table type ip size 500k expire 30s store conn_cur,conn_rate(10s),http_req_rate(10s),http_err_rate(10s)

# Enable tracking of src IP in the stick-table
tcp-request content track-sc0 src

Let’s decompose this configuration. First, we define a stick-table that stores IP addresses as keys. We define a maximum size for this table of 500,000 IPs, and we tell HAProxy to expire the records after 30 seconds. If the table gets filled, HAProxy will delete records following the LRU logic.

The stick-table will store a number of information associated with the IP address:

  • conn_cur is a counter of the concurrent connection count for this IP.
  • conn_rate(10s) is a sliding window that counts new TCP connections over a 10 seconds period
  • http_req_rate(10s) is a sliding window that counts HTTP requests over a 10 seconds period
  • http_err_rate(10s) is a sliding window that counts HTTP errors triggered by requests from that IP over a 10 seconds period

By default, the stick table declaration doesn’t do anything, we need to send data to it. This is what the tcp-request content track-sc0 src parameter does.

Now that we have tracking in place, we can write ACLs that run tests against the content of the table. The examples below evaluate several of these counters against arbitary limits. Tune these to your needs.

# Reject the new connection if the client already has 100 opened
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]over-100-active-connections, if { src_conn_cur ge 100 }

# Reject the new connection if the client has opened more than 100 connections in 10 seconds
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]over-100-connections-in-10-seconds, if { src_conn_rate ge 100 }

# Reject the connection if the client has passed the HTTP error rate
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]high-error-rate, if { sc0_http_err_rate() gt 100 }

# Reject the connection if the client has passed the HTTP request rate
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]high-request-rate, if { sc0_http_req_rate() gt 500 }

HAProxy provides a lot of flexibility on what can be tracked in a stick-table. Take a look at section 7.3.2. Fetching samples at Layer 4 from the doc to get a better idea.

6.2   Querying tables state in real time

Tables are named after the name of the frontend or backend they live in. Our frontend called fxa-https will have a table called fxa-https, that can be queried through the stat socket:

# echo "show table fxa-https" | socat unix:/var/lib/haproxy/stats -
# table: fxa-https, type: ip, size:512000, used:1
0x1aa3358: key= use=1 exp=29957 conn_rate(10000)=43 conn_cur=1 http_req_rate(10000)=42 http_err_rate(10000)=42

The line above shows a table entry for key, which is a tracked IP address. The other entries on the line show the status of various counters that we defined in the configuration.

6.3   Blacklists & Whitelists

Blacklist and whitelists are simple lists of IP addresses that are checked by HAProxy as early on as possible. Blacklist are checked at the beginning of the TCP connection, which allows for early connection drops, and also means that blacklisting an IP always takes precedence over any other rule, including the whitelist.

Whitelists are checked at the HTTP level, and allow to bypass ACLs and rate limiting.

# Blacklist: Deny access to some IPs before anything else is checked
tcp-request content reject if { src -f /etc/haproxy/blacklist.lst }

# Whitelist: Allow IPs to bypass the filters
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]whitelisted, if { src -f /etc/haproxy/whitelist.lst }
http-request allow if { src -f /etc/haproxy/whitelist.lst }

List files can contain IP addresses or networks in CIDR format.

List files are loaded into HAProxy at startup. If you add or remove IPs from a list, make sure to perform a soft reload.

haproxy -f /etc/haproxy/haproxy.cfg -c && sudo haproxy -f /etc/haproxy/haproxy.cfg -sf $(pidof haproxy)

6.4   Protect against slow clients (Slowloris attack)

Slowloris is an attack where a client very slowly sends requests to the server, forcing it to allocate resources to that client that are only not used. This attack is commonly used in DDoS, by clients that send their requests characters by characters. HAProxy can block these clients, by allocating a maximum amount of time a client can take to send a full request. This is done with the timeout http-request parameter.

# disconnect slow handshake clients early, protect from
# resources exhaustion attacks
timeout http-request 5s

7   URL filtering with ACLs

HAProxy has the ability to inspect requests before passing them to the backend. This is limited to query strings, and doesn’t support inspecting the body of a POST request. But we can already leverage this to filter out unwanted traffic.

The first thing we need, is a list of endpoints sorted by HTTP method. This can be obtained from the web application directly. Note that some endpoints, such as heartbeat should be limited to HAProxy, and thus blocked from clients.

For now, let’s ignore GET URL parameters, and only build a list of request paths, that we store in two files: one for GET requests, and one for POST requests.



In the HAProxy configuration, we can build ACLs around these files. The http-request deny method takes a condition, as described in the Haproxy documentation, section 7.2. Using ACLs to form conditions.

# Requests validation using ACLs ---
acl valid-get path -f /etc/haproxy/get_endpoints.lst
acl valid-post path -f /etc/haproxy/post_endpoints.lst

# block requests that don't match the predefined endpoints
http-request deny unless METH_GET valid-get or METH_POST valid-post

http-request deny does the job, and return a 403 to the client. But if you want more visibility on ACL activity, you may want to use a custom header as describe later in this section.

7.1   Filtering URL parameters on GET requests

While HAProxy supports regexes on URLs, writing regexes that can validate URL parameters is a path that leads to frustration and insanity. A much simpler approach consists of using the url_param ACL provided by HAProxy.

For example, take the NodeJS endpoint below:

  method: 'GET',
  path: '/verify_email',
  config: {
    validate: {
      query: {
        code: isA.string().max(32).regex(HEX_STRING).required(),
        uid: isA.string().max(32).regex(HEX_STRING).required(),
        service: isA.string().max(16).alphanum().optional(),
        redirectTo: isA.string()
  handler: function (request, reply) {
    return reply().redirect(config.contentServer.url + request.raw.req.url)

This endpoints receives requests on /verify_email with the parameters code, a 32 character hexadecimal, uid, a 32 character hexadecimal, service, a 16 character string, and redirectTo, a FQDN. However, only code and uid are required.

In the previous section, we validated that requests on /verify_email must use the method GET. Now we are taking the validation one step further, and blocking requests on this endpoint that do not match our prerequisite.

acl endpoint-verify_email path /verify_email
acl param-code urlp_reg(code) [0-9a-fA-F]{1,32}
acl param-uid urlp_reg(uid) [0-9a-fA-F]{1,32}
http-request deny if endpoint-verify_email !param-code or endpoint-verify_email !param-uid

The follow request will be accepted, everything else will be rejected with a HTTP error 403.


Using regexes to validate URL parameters is a powerful feature. Below is another example that matches an email addresses using case-insensitive regex:

acl endpoint-complete_reset_password path /complete_reset_password
acl param-email urlp_reg(email) -i ^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$
acl param-token urlp_reg(token) [0-9a-fA-F]{1,64}
http-request deny if endpoint-complete_reset_password !param-email or endpoint-complete_reset_password !param-token or endpoint-complete_reset_password !param-code

Note that we didn’t redefine param-code when we reused it in the http-request deny command. This is because ACL are defined globally for a frontend, and can be reused multiple times.

7.2   Filtering payloads on POST requests

POST requests are harder to validate, because they do not follow a predefined format, but also because the client could be sending the body over a long period of time, split over dozens of packets.

However, in the case of an API that only handles small POST payloads, we can at least verify the size of the payload sent by the client, and make sure that clients do not overload the backend with random data. This can be done using an ACL on the content-length header of the request. The ACL below discard requests that have a content-length larger than 5 kilo-bytes (which is already a lot of text).

# match content-length larger than 5kB
acl request-too-big hdr_val(content-length) gt 5000
http-request deny if METH_POST request-too-big

7.3   Marking instead of blocking

Blocking requests may be the preferred behavior in production, but only after a grace period that allows you to build a traffic profile, and fine tune your configuration. Instead of using http-request deny statements in the ACLs, we can insert a header with a description of the blocking decision. This header will be logged, and can be analyzed to verify that no legitimate traffic would be blocked.

As discussed in Logging in a separate frontend, HAProxy is unable to log request header that it has set itself. So make sure to log in a separate frontend if you use this technique.

The configuration below uses a custom header X-Haproxy-ACL. If an ACL matches, the header is set to the name of the ACL that matched. If several ACLs match, each ACL name is appended to the header, and separated by a comma.

At the end of the ACL evaluation, if this header is present in the request, we know that the request should be blocked.

In the fxa-https frontend, we replace the http-request deny paramameters with the following logic:

# ~~~ Requests validation using ACLs ~~~
# block requests that don't match the predefined endpoints
acl valid-get path -f /etc/haproxy/get_endpoints.lst
acl valid-post path -f /etc/haproxy/post_endpoints.lst
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]invalid-endpoint, unless METH_GET valid-get or METH_POST valid-post

# block requests on verify_email that do not have the correct params
acl endpoint-verify_email path /v1/verify_email
acl param-code urlp_reg(code) [0-9a-fA-F]{1,32}
acl param-uid urlp_reg(uid) [0-9a-fA-F]{1,32}
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]invalid-parameters, if endpoint-verify_email !param-code or endpoint-verify_email !param-uid

# block requests on complete_reset_password that do not have the correct params
acl endpoint-complete_reset_password path /v1/complete_reset_password
acl param-email urlp_reg(email) -i ^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$
acl param-token urlp_reg(token) [0-9a-fA-F]{1,64}
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]invalid-parameters, if endpoint-complete_reset_password !param-email or endpoint-complete_reset_password !param-token or endpoint-complete_reset_password !param-code

# block content-length larger than 500kB
acl request-too-big hdr_val(content-length) gt 5000
http-request add-header X-Haproxy-ACL %[req.fhdr(X-Haproxy-ACL,-1)]request-too-big, if METH_POST request-too-big

Note the %[req.fhdr(X-Haproxy-ACL,-1)] parameter, that retrieves the value of the latest occurence of the X-Haproxy-ACL header, so we can append to it and store it again. However, this will create multiple headers if more than one ACL is matched, but that’s OK because: – we can delete them before sending the request to the backend, using reqdel – the logging directive capture request header will only log the last occurence

X-Haproxy-ACL: over-100-active-connections,
X-Haproxy-ACL: over-100-active-connections,over-100-connections-in-10-seconds,
X-Haproxy-ACL: over-100-active-connections,over-100-connections-in-10-seconds,high-error-rate,
X-Haproxy-ACL: over-100-active-connections,over-100-connections-in-10-seconds,high-error-rate,high-request-rate,

Then, in the logger frontend, we check the value of the header, and block if needed.

# frontend use to log acl activity
frontend logger
        # if previous ACL didn't pass, and IP isn't whitelisted, block the request
        acl whitelisted req.fhdr(X-Haproxy-ACL) -m beg whitelisted,
        acl fail-validation req.fhdr(X-Haproxy-ACL) -m found
        http-request deny if !whitelisted fail-validation

8   HAProxy management

8.1   Enabling the stat socket

8.2   Collecting statistics

8.3   Analyzing errors

8.4   Parsing performance metrics from the logs

8.5   Soft reload

HAProxy supports soft configuration reload, that doesn’t drop connections. To perform a soft reload, call haproxy with the following command:

$ sudo /opt/haproxy -f /etc/haproxy/haproxy.cfg -sf $(pidof haproxy)

The old process will be replaced with a new one, that uses a fresh configuration. The logs will show the reload:

Mar  6 12:59:41 localhost haproxy[7603]: Proxy https started.
Mar  6 12:59:41 localhost haproxy[7603]: Proxy app started.
Mar  6 12:59:41 localhost haproxy[5763]: Stopping frontend https in 0 ms.
Mar  6 12:59:41 localhost haproxy[5763]: Stopping backend app in 0 ms.
Mar  6 12:59:41 localhost haproxy[5763]: Proxy https stopped (FE: 29476 conns, BE: 0 conns).
Mar  6 12:59:41 localhost haproxy[5763]: Proxy app stopped (FE: 0 conns, BE: 1746 conns).

9   Full HAProxy configuration

10   Building process

10.1   Static build

The script builds haproxy with statically linked OpenSSL and PCRE support.

10.2   Dynamic build

The script does the same as above, but links to PCRE and OpenSSL dynamically.

10.3   RPM build

Using the spec file in haproxy.spec and bash scripts in, we can build a RPM package using for the latest development version of HAProxy.


More information can be found on:

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