[proxy] More flexible container name -> hostname derivation

Provides to new two new flags: `--hostname-match <regexp>`
and `--hostname-replacement <replacement>`. When launching a container, its name
matched against regular expression `<regexp>`. Then, based on that match,
`<replacement>` will be used to generate a hostname, which will ultimately be
handed over to weaveDNS for registration.

The substitution is implemented with
https://golang.org/pkg/regexp/#Regexp.ReplaceAllString . Thus, references to
regexp substitution groups should be prepended with a dollar sign.

For instance, if we provide `--hostname-match '^aws-[0-9]+-(.*)$'` and
`--hostname-replacement 'my-app-$1'`, running a container named
`aws-12798186823-foo` through WeaveProxy will lead to WeaveDNS registering
`my-app-foo`.

Closes #1018

prog/weaveproxy/main.go

@@ -51,6 +51,8 @@ func main() {
 	mflag.BoolVar(&justVersion, []string{"#version", "-version"}, false, "print version and exit")
 	mflag.StringVar(&logLevel, []string{"-log-level"}, "info", "logging level (debug, info, warning, error)")
 	ListVar(&c.ListenAddrs, []string{"H"}, defaultListenAddrs, "addresses on which to listen")
+	mflag.StringVar(&c.HostnameMatch, []string{"-hostname-match"}, "(.*)", "Regexp pattern to apply on container names (e.g. '^aws-[0-9]+-(.*)$')")
+	mflag.StringVar(&c.HostnameReplacement, []string{"-hostname-replacement"}, "$1", "Expression to generate hostnames based on matches from --hostname-match (e.g. 'my-app-$1')")
 	mflag.BoolVar(&c.NoDefaultIPAM, []string{"#-no-default-ipam", "-no-default-ipalloc"}, false, "do not automatically allocate addresses for containers without a WEAVE_CIDR")
 	mflag.BoolVar(&c.NoRewriteHosts, []string{"no-rewrite-hosts"}, false, "do not automatically rewrite /etc/hosts. Use if you need the docker IP to remain in /etc/hosts")
 	mflag.StringVar(&c.TLSConfig.CACert, []string{"#tlscacert", "-tlscacert"}, "", "Trust certs signed only by this CA")

proxy/create_container_interceptor.go

@@ -58,7 +58,9 @@ func (i *createContainerInterceptor) InterceptRequest(r *http.Request) error {
 		if err := i.setWeaveWaitEntrypoint(container.Config); err != nil {
 			return err
 		}
-		if err := i.setWeaveDNS(&container, r.URL.Query().Get("name")); err != nil {
+		containerName := r.URL.Query().Get("name")
+		hostname := i.proxy.hostnameMatchRegexp.ReplaceAllString(containerName, i.proxy.HostnameReplacement)
+		if err := i.setWeaveDNS(&container, hostname); err != nil {
 			return err
 		}
 	}

proxy/proxy.go

@@ -15,11 +15,13 @@ import (
 )
 
 const (
-	defaultCaFile   = "ca.pem"
-	defaultKeyFile  = "key.pem"
-	defaultCertFile = "cert.pem"
-	dockerSock      = "/var/run/docker.sock"
-	dockerSockUnix  = "unix://" + dockerSock
+	defaultCaFile               = "ca.pem"
+	defaultKeyFile              = "key.pem"
+	defaultCertFile             = "cert.pem"
+	dockerSock                  = "/var/run/docker.sock"
+	dockerSockUnix              = "unix://" + dockerSock
+	substitutionPatternName     = "pattern"
+	substitutionReplacementName = "replacement"
 )
 
 var (
@@ -29,19 +31,22 @@ var (
 )
 
 type Config struct {
-	ListenAddrs    []string
-	NoDefaultIPAM  bool
-	NoRewriteHosts bool
-	TLSConfig      TLSConfig
-	Version        string
-	WithDNS        bool
-	WithoutDNS     bool
+	HostnameMatch       string
+	HostnameReplacement string
+	ListenAddrs         []string
+	NoDefaultIPAM       bool
+	NoRewriteHosts      bool
+	TLSConfig           TLSConfig
+	Version             string
+	WithDNS             bool
+	WithoutDNS          bool
 }
 
 type Proxy struct {
 	Config
-	client         *docker.Client
-	dockerBridgeIP string
+	client              *docker.Client
+	dockerBridgeIP      string
+	hostnameMatchRegexp *regexp.Regexp
 }
 
 func NewProxy(c Config) (*Proxy, error) {
@@ -65,6 +70,12 @@ func NewProxy(c Config) (*Proxy, error) {
 		p.dockerBridgeIP = string(dockerBridgeIP)
 	}
 
+	p.hostnameMatchRegexp, err = regexp.Compile(c.HostnameMatch)
+	if err != nil {
+		err := fmt.Errorf("Incorrect hostname match '%s': %s", c.HostnameMatch, err.Error())
+		return nil, err
+	}
+
 	return p, nil
 }
 

site/proxy.md

@@ -130,6 +130,35 @@ automatically if it is running at the point when they are started -
 see the [weaveDNS usage](weavedns.html#usage) section for an in-depth
 explanation of the behaviour and how to control it.
 
+Typicaly, the proxy will pass on container names as-is to [weaveDNS](weavedns.html)
+for registration. However, there are situations in which the final container
+name is out of the user's control (e.g. when using Docker orchestrators which
+append control/namespacing identifiers to the original container names).
+
+For those situations, the proxy provides two flags: `--hostname-match <regexp>`
+and `--hostname-replacement <replacement>`. When launching a container, its name
+matched against regular expression `<regexp>`. Then, based on that match,
+`<replacement>` will be used to generate a hostname, which will ultimately be
+handed over to weaveDNS for registration.
+
+For instance, if we launch the proxy using
+`--hostname-match '^aws-[0-9]+-(.*)$'` and `--hostname-replacement 'my-app-$1'`
+
+    host1$ weave launch-router && weave launch-dns && weave launch-proxy --hostname-match '^aws-[0-9]+-(.*)$' and --hostname-replacement 'my-app-$1'
+    host1$ eval "$(weave env)"
+
+then, running a container named `aws-12798186823-foo` will lead to weaveDNS registering
+hostname `my-app-foo` and not `aws-12798186823-foo`.
+
+    host1$ docker run -ti --name=aws-12798186823-foo ubuntu ping my-app-foo
+    PING my-app-foo.weave.local (10.32.0.2) 56(84) bytes of data.
+    64 bytes from my-app-foo.weave.local (10.32.0.2): icmp_seq=1 ttl=64 time=0.027 ms
+    64 bytes from my-app-foo.weave.local (10.32.0.2): icmp_seq=2 ttl=64 time=0.067 ms
+
+Note how regexp substitution groups should be prepended with a dollar sign
+(e.g. `$1`). For further details on the regular expression syntax please see
+[Google's re2 documentation](https://github.com/google/re2/wiki/Syntax).
+
 ## <a name="tls"></a>Securing the docker communication with TLS
 
 If you are

test/680_proxy_hostname_derivation.sh

@@ -0,0 +1,32 @@
+#! /bin/bash
+
+. ./config.sh
+
+C1=10.2.0.78
+C2=10.2.0.34
+C3=10.2.0.57
+CNAME1=qiuds71y827hdi-seeone-1io9qd9i0wd
+NAME1=seeone.weave.local
+CNAME2=124DJKSNK812-seetwo-128hbaJ881
+NAME2=seetwo.weave.local
+CNAME3=doesnotmatchpattern
+NAME3=doesnotmatchpattern.weave.local
+
+start_container() {
+  proxy docker_on $HOST1 run "$@" -dt $DNS_IMAGE /bin/sh
+}
+
+start_suite "Hostname derivation through container name substitutions"
+
+weave_on $HOST1 launch-dns 10.2.254.1/24
+weave_on $HOST1 launch-proxy --hostname-match '^[^-]+-(?P<appname>[^-]*)-[^-]+$' --hostname-replacement '$appname'
+
+start_container -e WEAVE_CIDR=$C1/24 --name=$CNAME1
+start_container -e WEAVE_CIDR=$C2/24 --name=$CNAME2
+start_container -e WEAVE_CIDR=$C3/24 --name=$CNAME3
+
+assert_dns_a_record $HOST1 $CNAME1 $NAME2 $C2
+assert_dns_a_record $HOST1 $CNAME2 $NAME3 $C3
+assert_dns_a_record $HOST1 $CNAME3 $NAME1 $C1
+
+end_suite

weave

@@ -37,6 +37,7 @@ weave launch-router [--password <password>] [--nickname <nickname>]
 weave launch-dns    [<addr>]
 weave launch-proxy  [-H <endpoint>] [--with-dns | --without-dns]
                       [--no-default-ipalloc] [--no-rewrite-hosts]
+                      [[--hostname-match <regexp>] [--hostname-replacement <replacement>]]
 weave connect       [--replace] [<peer> ...]
 weave forget        <peer> ...
 weave run           [--with-dns | --without-dns] [<addr> ...]