configuration of /etc/hosts to avoid "tango://[TANGO_HOST]:20000/dserver/[CLASS]/[INSTANCE] Not found" message

# 6 years ago
philippeg	Hi tangoers, into this post, Falek explained he found a way to solve "tango://[TANGO_HOST]:20000/dserver/[CLASS]/[INSTANCE] Not found". Fałek In Astor or Jive we had all machines like: IP address (IP address). We added DNS records for all the machines with DSes, but it didn't change. Only records in /etc/hosts changed it to host name (IP address). I'm not sure if it does matter to all machines except the tango host, we didn't noticed any other problems with that. Now the thing is shouldn't it be able to use those DNS records? The only place where /etc/hosts is specified into the doc is into https://tango-controls.readthedocs.io/en/latest/installation/vm/tangobox-9.2.html?highlight=%22%2Fetc%2Fhosts%22#network so I wonder if documentation should be updated or if this is only a side effect which should be fixed another way. It seems to me /etc/hosts configuration should not be mandatory to be configured if we have a configured DNS, since this is the goal of the DNS to give network hostname only once for all the network. I also confirm this solution (defining TANGO_HOST into /etc/hosts) make "dserver Not found" message disappear on our computers. 1°) Is there a way to avoid changing /etc/hosts when we have already a DNS? 2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue? Regards. - Philippe

# 6 years ago

Hi tangoers,

into this post, Falek explained he found a way to solve "tango://[TANGO_HOST]:20000/dserver/[CLASS]/[INSTANCE] Not found".

Fałek
In Astor or Jive we had all machines like: IP address (IP address). We added DNS records for all the machines with DSes, but it didn't change. Only records in /etc/hosts changed it to host name (IP address). I'm not sure if it does matter to all machines except the tango host, we didn't noticed any other problems with that.

Now the thing is shouldn't it be able to use those DNS records?

The only place where /etc/hosts is specified into the doc is into https://tango-controls.readthedocs.io/en/latest/installation/vm/tangobox-9.2.html?highlight=%22%2Fetc%2Fhosts%22#network so I wonder if documentation should be updated or if this is only a side effect which should be fixed another way.

It seems to me /etc/hosts configuration should not be mandatory to be configured if we have a configured DNS, since this is the goal of the DNS to give network hostname only once for all the network.

I also confirm this solution (defining TANGO_HOST into /etc/hosts) make "dserver Not found" message disappear on our computers.

1°) Is there a way to avoid changing /etc/hosts when we have already a DNS?
2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue?

Regards.

- Philippe

# 6 years ago
Reynald	philippeg into this post, Falek explained he found a way to solve "tango://[TANGO_HOST]:20000/dserver/[CLASS]/[INSTANCE] Not found". Fałek In Astor or Jive we had all machines like: IP address (IP address). We added DNS records for all the machines with DSes, but it didn't change. Only records in /etc/hosts changed it to host name (IP address). I'm not sure if it does matter to all machines except the tango host, we didn't noticed any other problems with that. Now the thing is shouldn't it be able to use those DNS records? It should be able to use those DNS records if the network/DNS configuration is correct. Having DNS records is probably not enough if the host is not properly configured to do some queries to the nameserver. There are several configuration files involved there (warning: I am no sys admin and I don't pretend to be an expert in DNS configuration), on Linux at least: /etc/nsswitch.conf /etc/resolv.conf A DNS cache daemon can be involved too (nscd) and can really improve the performances. philippeg The only place where /etc/hosts is specified into the doc is into https://tango-controls.readthedocs.io/en/latest/installation/vm/tangobox-9.2.html?highlight=%22%2Fetc%2Fhosts%22#network so I wonder if documentation should be updated or if this is only a side effect which should be fixed another way. It seems to me /etc/hosts configuration should not be mandatory to be configured if we have a configured DNS, since this is the goal of the DNS to give network hostname only once for all the network. Right you are! philippeg I also confirm this solution (defining TANGO_HOST into /etc/hosts) make "dserver Not found" message disappear on our computers. 1°) Is there a way to avoid changing /etc/hosts when we have already a DNS? Ensure your DNS is properly configured and your hosts are properly configured to use the DNS. In our case, our TANGO_HOST is not listed in /etc/hosts. philippeg 2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue? "The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network? Cheers, Reynald Rosenberg's Law: Software is easy to make, except when you want it to do something new. Corollary: The only software that's worth making is software that does something new.

# 6 years ago

Reynald

philippeg
into this post, Falek explained he found a way to solve "tango://[TANGO_HOST]:20000/dserver/[CLASS]/[INSTANCE] Not found".

Fałek
In Astor or Jive we had all machines like: IP address (IP address). We added DNS records for all the machines with DSes, but it didn't change. Only records in /etc/hosts changed it to host name (IP address). I'm not sure if it does matter to all machines except the tango host, we didn't noticed any other problems with that.

Now the thing is shouldn't it be able to use those DNS records?

It should be able to use those DNS records if the network/DNS configuration is correct.
Having DNS records is probably not enough if the host is not properly configured to do some queries to the nameserver.
There are several configuration files involved there (warning: I am no sys admin and I don't pretend to be an expert in DNS configuration), on Linux at least:

/etc/nsswitch.conf
/etc/resolv.conf

A DNS cache daemon can be involved too (nscd) and can really improve the performances.

philippeg
The only place where /etc/hosts is specified into the doc is into https://tango-controls.readthedocs.io/en/latest/installation/vm/tangobox-9.2.html?highlight=%22%2Fetc%2Fhosts%22#network so I wonder if documentation should be updated or if this is only a side effect which should be fixed another way.

It seems to me /etc/hosts configuration should not be mandatory to be configured if we have a configured DNS, since this is the goal of the DNS to give network hostname only once for all the network.

Right you are!

philippeg
I also confirm this solution (defining TANGO_HOST into /etc/hosts) make "dserver Not found" message disappear on our computers.

1°) Is there a way to avoid changing /etc/hosts when we have already a DNS?

Ensure your DNS is properly configured and your hosts are properly configured to use the DNS.
In our case, our TANGO_HOST is not listed in /etc/hosts.

philippeg
2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue?

"The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network?

Cheers,
Reynald

Rosenberg's Law: Software is easy to make, except when you want it to do something new.
Corollary: The only software that's worth making is software that does something new.

# 6 years ago
philippeg	Thank you, I will check this with our sysadmin. Reynald philippeg 2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue? "The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network? 2d solution: I mean that the hardware is not yet accessible through an IP and the DS can not access its IP through the network. - Philippe

# 6 years ago

philippeg

Thank you, I will check this with our sysadmin.

Reynald
philippeg
2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue?

"The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network?

2d solution: I mean that the hardware is not yet accessible through an IP and the DS can not access its IP through the network.

- Philippe

# 6 years ago
lorenzo	philippeg Thank you, I will check this with our sysadmin. Reynald philippeg 2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue? "The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network? 2d solution: I mean that the hardware is not yet accessible through an IP and the DS can not access its IP through the network. This should not be an issue, except that, depending on the implementation, the TANGO device may be stuck in the init_device() method waiting for the IP to become reachable… thus not "published" on the TANGO DB. However, if you're using the hostname for the equipment as well, and not the IP, you should check that that is resolved by your DNS as well or you'll trigger quite a bit of network traffic. Lorenzo

# 6 years ago

lorenzo

philippeg
Thank you, I will check this with our sysadmin.

Reynald
philippeg
2°) I saw this error message appearing on another CLASS than starter (the IP of the hardware is not yet accessible through network), is it normal or do I have an(other) network configuration issue?

"The IP of the hardware is not accessible through the network". Do you mean the host where the device server is running is not available on the network or the hardware the device server is trying to access is not available on the network?

2d solution: I mean that the hardware is not yet accessible through an IP and the DS can not access its IP through the network.

This should not be an issue, except that, depending on the implementation, the TANGO device may be stuck in the init_device() method waiting for the IP to become reachable… thus not "published" on the TANGO DB.
However, if you're using the hostname for the equipment as well, and not the IP, you should check that that is resolved by your DNS as well or you'll trigger quite a bit of network traffic.
Lorenzo

# 6 years ago
philippeg	I'll check that. Is there any behavior where we need to use IP? For instance, I remember a DS needing to enter the IP as properties and I think remembering it did not accept hostname. Did you had some similar issues or should I check again? Thank you. - Philippe

# 6 years ago
lorenzo	philippeg I'll check that. Is there any behavior where we need to use IP? For instance, I remember a DS needing to enter the IP as properties and I think remembering it did not accept hostname. Did you had some similar issues or should I check again? Thank you. Well, that depends on the developer using gethostby[name\|address] in the code… but if you go for the hostname that should be resolved by the DNS or the hosts file, e.g. a proper host configuration The IP doesn't require resolving. Anyhow, you really want to rely on a proper host configuration anyway, e.g not rely on the IP shortcut (even if you can config by IP for convenience).

# 6 years ago

lorenzo

philippeg
I'll check that.
Is there any behavior where we need to use IP?
For instance, I remember a DS needing to enter the IP as properties and I think remembering it did not accept hostname. Did you had some similar issues or should I check again?
Thank you.

Well, that depends on the developer using gethostby[name|address] in the code… but if you go for the hostname that should be resolved by the DNS or the hosts file, e.g. a proper host configuration The IP doesn't require resolving. Anyhow, you really want to rely on a proper host configuration anyway, e.g not rely on the IP shortcut (even if you can config by IP for convenience).

# 6 years ago
philippeg	Thank you for these explanations. I will check in the DS how is accessed each host, but I understand there is not impossibility on this topic. - Philippe