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183 lines
3.6 KiB
Ruby
Executable File
183 lines
3.6 KiB
Ruby
Executable File
#!/usr/bin/env ruby
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# frozen_string_literal: true
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require 'ipaddr'
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require 'resolv'
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require 'time'
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require 'socket'
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REFRESH_SECONDS = 30
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HOSTS_PATH = "/etc/hosts"
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CRITICAL_HOST_ENV_VARS = %w{
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DISCOURSE_DB_HOST
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DISCOURSE_DB_REPLICA_HOST
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DISCOURSE_REDIS_HOST
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DISCOURSE_REDIS_SLAVE_HOST
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}
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def log(msg)
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STDERR.puts "#{Time.now.iso8601}: #{msg}"
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end
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def error(msg)
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log(msg)
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end
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def swap_address(hosts, name, ips)
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new_file = []
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hosts.split("\n").each do |line|
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line.strip!
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if line[0] != '#'
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_, hostname = line.split(/\s+/)
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next if hostname == name
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end
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new_file << line
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new_file << "\n"
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end
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ips.each do |ip|
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new_file << "#{ip} #{name} # AUTO GENERATED: #{Time.now.iso8601}\n"
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end
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new_file.join
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end
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def hosts_entries(dns, name)
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host = ENV[name]
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results = dns.getresources(host, Resolv::DNS::Resource::IN::A)
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results.concat dns.getresources(host, Resolv::DNS::Resource::IN::AAAA)
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results.map do |result|
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"#{result.address}"
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end
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end
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def send_counter(name, description, labels, value)
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host = "localhost"
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port = ENV.fetch("DISCOURSE_PROMETHEUS_COLLECTOR_PORT", 9405).to_i
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if labels
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labels = labels.map do |k, v|
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"\"#{k}\": \"#{v}\""
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end.join(",")
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else
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labels = ""
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end
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json = <<~JSON
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{
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"_type": "Custom",
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"type": "Counter",
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"name": "#{name}",
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"description": "#{description}",
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"labels": { #{labels} },
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"value": #{value}
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}
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JSON
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payload = +"POST /send-metrics HTTP/1.1\r\n"
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payload << "Host: #{host}\r\n"
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payload << "Connection: Close\r\n"
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payload << "Content-Type: application/json\r\n"
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payload << "Content-Length: #{json.bytesize}\r\n"
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payload << "\r\n"
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payload << json
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socket = TCPSocket.new host, port
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socket.write payload
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socket.flush
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result = socket.read
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first_line = result.split("\n")[0]
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if first_line.strip != "HTTP/1.1 200 OK"
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error("Failed to report metric #{result}")
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end
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socket.close
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rescue => e
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error("Failed to send metric to Prometheus #{e}")
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end
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def report_success
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send_counter('critical_dns_successes_total', 'critical DNS resolution success', nil, 1)
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end
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def report_failure(errors)
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errors.each do |host, count|
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send_counter('critical_dns_failures_total', 'critical DNS resolution failures', host ? { host: host } : nil, count)
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end
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end
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@vars = CRITICAL_HOST_ENV_VARS.map do |name|
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begin
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host = ENV[name]
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next if !host || host.length == 0
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IPAddr.new(ENV[name])
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nil
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rescue IPAddr::InvalidAddressError, IPAddr::AddressFamilyError
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name
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end
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end.compact
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def loop
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errors = Hash.new(0)
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Resolv::DNS.open do |dns|
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dns.timeouts = 2
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resolved = {}
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hosts = @vars.each do |var|
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host = ENV[var]
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begin
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entries = hosts_entries(dns, var)
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rescue => e
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error("Failed to resolve DNS for #{name} - #{e}")
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errors[host] += 1
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end
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if entries&.length > 0
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resolved[host] = entries
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else
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error("Failed to find any DNS entry for #{var} : #{ENV[var]}")
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errors[host] += 1
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end
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end
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hosts_content = File.read(HOSTS_PATH)
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hosts = Resolv::Hosts.new(HOSTS_PATH)
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changed = false
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resolved.each do |name, ips|
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if hosts.getaddresses(name).map(&:to_s).sort != ips.sort
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log("IP addresses for #{name} changed to #{ips}")
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hosts_content = swap_address(hosts_content, name, ips)
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changed = true
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end
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end
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if changed
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File.write(HOSTS_PATH, hosts_content)
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end
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end
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rescue => e
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error("Failed to access DNS - #{e}")
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errors[nil] = 1
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ensure
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if errors == {}
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report_success
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else
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report_failure(errors)
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end
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end
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while true
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loop
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sleep REFRESH_SECONDS
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end
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