contrib: systemd unit files and docs

This commit contains `systemd` unit file and the documentation
describing how to run `gobgp` as `systemd` managed service
on CentOS/RHEL Linux distribution.

Signed-off-by: Paul Greenberg <greenpau@outlook.com>

3 files changed, 134 insertions, 0 deletions

diff --git a/contrib/centos/README.md b/contrib/centos/README.md
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index 00000000..a8416b45
--- /dev/null
+++ b/contrib/centos/README.md
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+# GoBGP systemd Integration for CentOS
+
+The following document describes how to manage `gobgp` with `systemd`.
+
+Download `gobgp` binaries, unpack them, and put them `/usr/bin/`:
+
+```bash
+mkdir -p /tmp/gobgp
+cd /tmp/gobgp && curl -s -L -O https://github.com/osrg/gobgp/releases/download/v1.31/gobgp_1.31_linux_amd64.tar.gz
+tar xvzf gobgp_1.31_linux_amd64.tar.gz
+mv gobgp /usr/bin/
+mv gobgpd /usr/bin/
+```
+
+Grant the capability to bind to system or well-known ports, i.e. ports with
+numbers `0–1023`, to `gobgpd` binary:
+
+```bash
+/sbin/setcap cap_net_bind_service=+ep /usr/bin/gobgpd
+/sbin/getcap /usr/bin/gobgpd
+```
+
+First, create a system account for `gobgp` service:
+
+```bash
+groupadd --system gobgpd
+useradd --system -d /var/lib/gobgpd -s /bin/bash -g gobgpd gobgpd
+mkdir -p /var/{lib,run,log}/gobgpd
+chown -R gobgpd:gobgpd /var/{lib,run,log}/gobgpd
+mkdir -p /etc/gobgpd
+chown -R gobgpd:gobgpd /etc/gobgpd
+```
+
+Paste the below to create `gobgpd` configuration file. The `router-id` in this
+example is the IP address of the interface the default route of the host is
+pointing to.
+
+```bash
+DEFAULT_ROUTE_INTERFACE=$(cat /proc/net/route | cut -f1,2 | grep 00000000 | cut -f1)
+DEFAULT_ROUTE_INTERFACE_IPV4=$(ip addr show dev $DEFAULT_ROUTE_INTERFACE | grep "inet " | sed "s/.*inet //" | cut -d"/" -f1)
+BGP_AS=65001
+BGP_PEER=10.0.255.1
+cat << EOF > /etc/gobgpd/gobgpd.conf
+[global.config]
+  as = $BGP_AS
+  router-id = "$DEFAULT_ROUTE_INTERFACE_IPV4"
+
+[[neighbors]]
+  [neighbors.config]
+    neighbor-address = "$BGP_PEER"
+    peer-as = $BGP_AS
+EOF
+chown -R gobgpd:gobgpd /etc/gobgpd/gobgpd.conf
+```
+
+Next, copy the `systemd` unit file, i.e. `gobgpd.service`, in this directory
+to `/usr/lib/systemd/system/`:
+
+```bash
+cp gobgpd.service /usr/lib/systemd/system/
+```
+
+Next, enable and start the `gobgpd` services:
+
+```bash
+systemctl enable gobgpd
+systemctl start gobgpd
+```
+
+If necessary, create an `iptables` rule to allow traffic to `gobgpd` service:
+
+```bash
+iptables -I INPUT 4 -p tcp -m state --state NEW --dport 179 -j ACCEPT
+```
+
+Also, add the following rule into `INPUT` chain in `/etc/sysconfig/iptables`:
+
+```plaintext
+# BGP
+-A INPUT -p tcp -m state --state NEW -m tcp --dport 179 -j ACCEPT
+```
+
+Check the status of the services:
+
+```bash
+systemctl status gobgpd
+```
+
+The logs are available via `journald`:
+
+```bash
+journalctl -u gobgpd.service --since today
+journalctl -u gobgpd.service -r
+```
+
+A user may interract with GoBGP daemon via `gobgp` tool:
+
+```bash
+# gobgp global
+AS:        65001
+Router-ID: 10.0.255.1
+Listening Port: 179, Addresses: 0.0.0.0, ::
+
+# gobgp global rib summary
+Table ipv4-unicast
+Destination: 0, Path: 0
+
+# gobgp neighbor
+Peer            AS Up/Down State       |#Received  Accepted
+10.0.255.1   65001   never Active      |        0
+```
diff --git a/contrib/centos/add_gobgpd_account.sh b/contrib/centos/add_gobgpd_account.sh
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+groupadd --system gobgpd
+useradd --system -d /var/lib/gobgpd -s /bin/bash -g gobgpd gobgpd
+mkdir -p /var/{lib,run,log}/gobgpd
+chown -R gobgpd:gobgpd /var/{lib,run,log}/gobgpd
+mkdir -p /etc/gobgpd
+chown -R gobgpd:gobgpd /etc/gobgpd
diff --git a/contrib/centos/gobgpd.service b/contrib/centos/gobgpd.service
new file mode 100644
index 00000000..5aac6d7b
--- /dev/null
+++ b/contrib/centos/gobgpd.service
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+[Unit]
+Description=GoBGP Routing Daemon
+Wants=network.target
+After=network.target
+
+[Service]
+Type=simple
+ExecStartPre=/usr/bin/gobgpd -f /etc/gobgpd/gobgpd.conf -d
+ExecStart=/usr/bin/gobgpd -f /etc/gobgpd/gobgpd.conf
+ExecReload=/usr/bin/gobgpd -r
+StandardOutput=journal
+StandardError=journal
+User=gobgpd
+Group=gobgpd
+
+[Install]
+WantedBy=multi-user.target