Configures TCP pacing on boot depending on site's uplink speed (#138)

* Modifies cloud-config to write two new files to set up TCP pacing and one new service unit file to run the pacing configuration script.

* Removes trying to set net.core.default_qdisc=fq in /etc/sysctl.d, since changes don't need to be persisted since machines reinitialize 100% on every boot anyway. Use replace instead of add in tc command.

* Removes the set-tc-qdisc.service, since this functionality is now handled by the configure-tc-fq.service.

* Adds a better systemd service unit description for configure-tc-fq.service.

* Uses long options with curl. Adds a small echo so that logs should some useful output on success.

* Set maxrate for 1g site to 1gbit, per @stephen-soltesz request in PR.

configs/stage3_coreos/resources/cloud-config.yml

@@ -24,14 +24,6 @@ coreos:
         Type=oneshot
         ExecStart=/usr/share/oem/generate_network_config.sh /etc/systemd/network/00-eth0.network
 
-    # Replaces eth0's qdisc with fq.
-    - name: set-tc-qdisc.service
-      command: start
-      content: |
-        [Service]
-        Type=oneshot
-        ExecStart=/usr/sbin/tc qdisc replace dev eth0 root fq
-
     # Restarts the networkd service using our new config.
     - name: systemd-networkd.service
       command: restart
@@ -174,6 +166,41 @@ coreos:
         Type=oneshot
         ExecStart=/usr/sbin/modprobe tcp_bbr
 
+    # A unit to run the script that configures Fair Queue ("TCP pacing") for eth0.
+    - name: configure-tc-fq.service
+      command: start
+      enable: true
+      content: |
+        [Unit]
+        Description=Configures TCP pacing properly depending on the site's uplink speed
+        Requires=network-online.target
+        After=systemd-networkd-wait-online.service systemd-resolved.service format-cache.service
+
+        [Service]
+        Type=oneshot
+        ExecStart=/opt/bin/configure_tc_fq.sh
+
+write_files:
+  - path: /opt/bin/configure_tc_fq.sh
+    permissions: 0744
+    owner: root:root
+    content: |
+      #!/bin/bash
+      SITE=$(dnsdomainname | cut -d. -f1)
+      SPEED=$(curl --silent --show-error --location \
+          https://siteinfo.mlab-oti.measurementlab.net/v1/sites/switches.json \
+          | jq -r ".${SITE}.uplink_speed")
+      if [[ "${SPEED}" == "10g" ]]; then
+        MAXRATE="8gbit"
+      elif [[ "${SPEED}" == "1g" ]]; then
+        MAXRATE="1gbit"
+      else
+        echo "Unknown uplink speed '${SPEED}'. Not configuring default qdisc for eth0."
+        exit 1
+      fi
+      /sbin/tc qdisc replace dev eth0 root fq maxrate "${MAXRATE}"
+      echo "Set maxrate for qdisc fq on dev eth0 to: ${MAXRATE}"
+
 # TODO: collect list of ssh keys from a metadata service during post-boot setup.
 ssh_authorized_keys:
  - "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCvIKeMHcEO1xnTmEdMY6E9Y4pBdGBCDXZnuQC5ZPjNQr9IG3ytw0OxwyCObAzSr+WOymYv6Cwm4Ckz2jc/bWygzWJH+DMdldZe7HVQu4YxuegqahIkB0D1OzaZGNctBgTp9bmpWGxyek7U8ff7GTiFqhcms4Oer4rdd0gqUhmv3LnRWQqrIDblrBosHBED/zXgjbOj3beWCA3xHDCaui/gkbmp0J2jzCnlsc7eSI0d6Jro2UhbiS2ssxVQsLViLh5okJJeb2JyzbLbcpselUg9DSwSk0pFH/wHL0usjvBisF/fEP8eQ1svq6N6gncvPlgoJaSvtACmDvIFkU4baA2v pboothe@pboothe3.nyc.corp.google.com"