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middleware/kubernetes: Server side path lookups (#750)

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* initial commit

* add config options

* add readme

* rewording

* revert unlreated change

* normalize host domain path

* add ndots opt, allow > 1 host domains, pull host domains from resolv.conf

* implementing review feedback

* update readme

* use dns lib, config format, defaults

* Correct autopath example.
This commit is contained in:
Chris O'Haver
2017-06-28 18:44:30 -04:00
committed by John Belamaric
parent 817f3960b8
commit edf71fb168
6 changed files with 407 additions and 51 deletions
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52
middleware/kubernetes/README.md
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@@ -121,6 +121,58 @@ kubernetes coredns.local {
# Each line consists of the name of the federation, and the domain.
federation myfed foo.example.com
# autopath [NDOTS [RESPONSE [RESOLV-CONF]]
#
# Enables server side search path lookups for pods. When enabled, coredns
# will identify search path queries from pods and perform the remaining
# lookups in the path on the pod's behalf. The search path used mimics the
# resolv.conf search path deployed to pods. E.g.
#
# search ns1.svc.cluster.local svc.cluster.local cluster.local foo.com
#
# If no domains in the path produce an answer, a lookup on the bare question
# will be attempted.
#
# A successful response will contain a question section with the original
# question, and an answer section containing the record for the question that
# actually had an answer. This means that the question and answer will not
# match. For example:
#
# # host -v -t a google.com
# Trying "google.com.default.svc.cluster.local"
# ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50957
# ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
#
# ;; QUESTION SECTION:
# ;google.com.default.svc.cluster.local. IN A
#
# ;; ANSWER SECTION:
# google.com. 175 IN A 216.58.194.206
#
#
# NDOTS (default: 0) This provides an adjustable threshold to
# prevent server side lookups from triggering. If the number of dots before
# the first search domain is less than this number, then the search path will
# not executed on the server side.
#
# RESPONSE (default: SERVFAIL) RESPONSE can be either NXDOMAIN, SERVFAIL or
# NOERROR. This option causes coredns to return the given response instead of
# NXDOMAIN when the all searches in the path produce no results. Setting this
# to SERVFAIL or NOERROR should prevent the client from fruitlessly continuing
# the client side searches in the path after the server already checked them.
#
# RESOLV-CONF (default: /etc/resolv.conf) If specified, coredns uses this
# file to get the host's search domains. CoreDNS performs a lookup on these
# domains if the in-cluster search domains in the path fail to produce an
# answer. If not specified, the values will be read from the local resolv.conf
# file (i.e the resolv.conf file in the pod containing coredns).
#
# Enabling autopath causes coredns to use more memory since it needs to
# maintain a watch on all pods. If autopath and "pods verified" mode are
# both enabled, they will share the same watch. I.e. enabling both options
# should have an equivalent memory impact of just one.
autopath 0 SERVFAIL /etc/resolv.conf
# fallthrough
#
# If a query for a record in the cluster zone results in NXDOMAIN,